Bonding objects together

ABSTRACT

A method of bonding a first object to a second object includes the steps of: providing the first object including thermoplastic material in a solid state, providing the second object including a proximal surface, applying a mechanical pressing force and a mechanical excitation capable to liquefy the thermoplastic material until a flow portion of the thermoplastic material is flowable and penetrates into structures of the second object, and stopping the mechanical excitation and letting the thermoplastic material resolidify to yield a positive-fit connection between the first and the second object. The second object has a region of low density, wherein the protrusion penetrates the region of low density at least partly before the thermoplastic material is made flowable, and wherein the first object includes a protruding portion after the step of letting the thermoplastic material resolidify, the protruding portion at least partly penetrates the region of low density.

BACKGROUND OF THE INVENTION Field of the Invention

The invention is in the fields of mechanical engineering andconstruction, especially mechanical construction, for example automotiveengineering.

Description of Related Art

Devices used or produced in automotive, aviation and other industriesinclude surfaces that need to fulfil physical demands given by the useror authorities. Such demands concern optical, acoustic, thermal andmechanical properties, in particular. For example, the quality and valueof a device is linked to the visual impression given by exteriorsurfaces, the generation of noise due to vibration of or within thedevice needs to be limited and/or adapted, and the surface needs togenerate a specific feeling and/or a specific resistance againstdegradation due to use of the device.

Covers that are attached to the surfaces are one approach to meet thedemands. Thereby, two methods to attach the cover to the surfacedirectly or to attach a connector to the cover with which the cover canbe attached to the surface have prevailed.

A first method uses adhesives. However, adhesives are disadvantageous interms of long term stability. In particular, if an adhesive is used forthe attachment of a cover with or to a porous and/or fibrous surface forexample, the stability can be poor because the outmost portions of thefibers and/or pores are embedded in the adhesive and contribute to thebonding, only.

Further, the use of adhesive is time consuming (e.g., due to hardeningprocesses), needs generally the treatment of an extensive area and canbe limited to certain body geometries as it is the case for frictionwelding, for example.

A second method uses fasteners that penetrate the cover, usually.Rivets, nails and screws are examples of such fasteners. The use offasteners as well as related approaches that are based on through goingholes produced during the attachment or pre-drilled are disadvantageousin terms of optical and acoustic properties, at least.

Hence, there is need for alternative methods to bond objects together,in particular to bond covers with specific physical properties tosurfaces of devices such as vehicles and machines.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method for bondingobjects together, the method overcoming disadvantages of prior artmethods.

In particular, it is an object of the invention to provide a method forbonding a first object to a second object wherein one of the objects hasa specific density profile. The density profile results from demandsconcerning for at least one of acoustic (e.g., damping) properties,thermal (e.g., insulating) properties, mechanical properties and opticalproperties, for example.

The mechanical properties can include the generation of a specific,e.g., soft, feeling and/or a high resistance against degradation due tofrequent use. The optical properties can rely on the demand for asurface that is unaffected by the bonding of the first object to thesecond object.

A method according to the invention is suitable for bonding a firstobject to a second object. In its basic embodiment, the method includesthe steps of:

-   -   Providing the first object, wherein the first object extends        between a proximal end and a distal end, wherein the first        object includes thermoplastic material in a solid state.    -   Providing the second object including a proximal surface.    -   Applying a mechanical pressing force and a mechanical excitation        capable to liquefy the thermoplastic material to at least one of        the first and second object until a flow portion of the        thermoplastic material is flowable and penetrates into        structures of the second object.    -   Stopping the mechanical excitation and letting the thermoplastic        material resolidify to yield a positive-fit connection between        the first and the second object.

The method in its basic embodiment is characterized in that the secondobject provided includes a region of low density and in that the distalend penetrates the region of low density at least partly before thethermoplastic material is made flowable.

The region of low density that is at least partly penetrated by thedistal end before the thermoplastic material is made flowable is notnecessarily the region of lowest density of the second object. This alsomeans that the first object is not necessarily anchored in the region oflowest density of the second object.

For example, the region of low density that is at least partlypenetrated by the distal end can form a base for a region of even lowerdensity that forms for example an exposed surface of the first object.Such embodiments can be present in cases in which a part of a car bodyforms part of the first object and a cover forms the second object, forexample.

Preferred embodiments can include at least one of the followingfeatures:

-   -   The step of applying the mechanical excitation includes applying        mechanical oscillations along an axis that runs at an angle to        the proximal surface and the proximal surface of the second        object provided is of low density. In this embodiment at least,        the region of low density extends normal to, this means distally        from, the proximal surface. The region of low density can be a        proximal region of low density. The proximal region of low        density can include the proximal surface.    -   The first object provided includes a first object body and at        least one protrusion distally of the first object body, wherein        the protrusion forms the distal end and includes the        thermoplastic material in a solid state.        -   In this embodiment, it is the protrusion (or a plurality of            protrusions) that penetrates the region of low density at            least partly before the thermoplastic material is made            flowable. Further the first object includes a protruding            portion after the step of letting the thermoplastic material            resolidify, wherein the protruding portion penetrates the            region of low density at least partly.    -   A step of changing a compressive strength of the region of low        density at least locally. In this context, the term “compressive        strength” is referred to the maximal force per square millimetre        generated by an area before the area is displaced, this means        before the material defining the area is (further) compressed.        Hence, the compressive strength can also be seen as a resistance        against further compression or as a stiffness.

The compressive strength corresponds to the stress as measured in astress-strain experiment, for example.

The change in compressive strength (stress) can be such that themechanical pressing force and the mechanical excitation applied cancause the liquefaction of the thermoplastic material. In other words,the region of low density can be such that it is not able to provide thecompressive strength needed to liquefy the thermoplastic material in thestep of applying the mechanical pressing force and the mechanicalexcitation without a change of the compressive strength.

The step of changing the compressive strength of the region of lowdensity at least locally can be carried out until a critical compressivestrength is generated, this means until the compressive strength neededto liquefy the thermoplastic material with the mechanical pressing forceand the mechanical excitation applied is reached.

The change of the compressive strength needed to cause liquefaction ofthe thermoplastic material in the step of applying the mechanicalpressing force and the mechanical excitation can depend on themechanical pressing force and the mechanical excitation applied.

In particular, the change in compressive strength is an increase incompressive strength.

In many embodiments, the increase in compressive strength is caused byan at least local compression of the region of low density. In otherwords, the method can include a step of compressing the region of lowdensity at least locally.

In particular, the compressive strength can depend on a densification ofthe region of low density, wherein the densification is caused by thecompression.

The region of low density can be compressed by the mechanical pressingforce applied for liquefying the thermoplastic material.

In the step of applying the mechanical pressing force and the mechanicalexcitation for liquefying the thermoplastic material, the mechanicalexcitation can be applied, this means switched on, after the compressionof the region of low density has caused an increase of the compressivestrength that is sufficient for the liquefaction of the thermoplasticmaterial with the mechanical pressing force and the mechanicalexcitation applied.

The step of changing the compressive strength of the region of lowdensity at least locally or the step of compressing the region of lowdensity at least locally can make the method suitable for bonding thefirst object to the second object by the positive-fit connection betweenthe first and second object, wherein the positive-fit connection isestablished in a region of the second object that corresponds to theregion of low density before bonding the first object to the secondobject.

In embodiments, the region of low density is formed by an essentiallyincoherent material, this means a material including constituents thatinteract weakly only, for example when exposed to an external force suchas a compressing force.

A material including or consisting of fibers that are under the appliedforce movable relative to each other to some extend is an example of anincoherent material.

There is no need that the weak interaction between the constituents ispresent in the second object as provided. Rather, the weak interactioncan be a result of a force acting on the second object during themethod. Such a force can cause a breakup of the connection between theconstituents. For example, the material can include fibers that havelocally been connected by a binder material, e.g., a resin powder ormelt-fibers combined with a heat treatment, to define a specifieddensity of the material.

In many embodiments, the distal end penetrating into or through thesecond object is a protrusion or a plurality of protrusions.

In this text, any relative arrangement within objects, items, devices,etc., and any relative arrangement between objects, items, devices etc.is given relative to an origin situated in the middle of the firstobject. When not otherwise stated, the surface of an object that isarranged closest to the origin is called the proximal surface of theobject and a corresponding surface of the object, for example acorresponding surface arranged on the opposite side of the object, iscalled the distal surface. In the case of the first object, the surfacedirected to a proximal surface of another object to which the firstobject is to be set in contact and/or—as the case may be—to be bonded iscalled the distal surface of the first object. In other words, proximalsurfaces are always set in contact and/or—as the case may be—bonded todistal surfaces during the method. Consequently, the protrusion(s)is/are arranged distally on the first object.

In many embodiments, a protruding portion means that there is a portionof the protrusion left after the step of letting the thermoplasticmaterial resolidify, wherein the portion, this means the protrudingportion, is not restricted to the outmost region of the second object,but extends into the volume of the second object. Being left means thatthe material defining the protruding portion has not penetrate into thestructures of the second object.

How far the protruding portion penetrates into the second object dependson the application. However, the penetration depths of the protrudingportion normal to the proximal surface of the second object is oftenlarger than an extension of the protruding portion in a directionparallel to the proximal surface of the second object. This means, theratio between the extension normal to the proximal surface and theextension parallel to the proximal surface is at least 1, in particularbetween 1 and 5, for example between 1.5 and 4 or between 2 and 3.

Slightly different definitions of the protruding portion and/or otherfeatures that characterise the protrusion portion are given below.

In this text, a surface or region of low density means that it is atleast one of porous, fibrous and soft and/or that it includes aplurality of structures, voids, openings etc. The structures, voidsand/or openings are capable for damping, in particular acoustic dampingand/or vibration damping, for example.

In embodiments, in particular in embodiments of the method including thestep of compressing the region of low density as described below indetail, the region of low density is compressible along an axis alongwhich the mechanical pressing force is applied during the step ofapplying the mechanical pressing force and the mechanical excitation.The compression can lead to a reduction of a thickness of the region oflow density by 10-90%, for example, wherein the thickness is measuredalong the axis at which the mechanical pressing force is applied. Inparticular, the thickness can be reduced by 30-90%, for example by60-80%, or by 20-80%, for example by 30-70%.

A compression ratio is another measure for the compression of the regionof low density. In particular, the compression ratio is an appropriatemeasure when local compression is considered. The compression ratio inthe region of the protrusion can be between 1.1 and 10, in particularbetween 1.25 and 5, for example between 1.4 and 3.3.

The material or material composition forming the region of low densitycan be such that it can be locally compressed. For example, a localmechanical load, e.g., generated by the protrusion of the first objector a protruding region of an item attached to the second object, cancause the local compression of the region of low density.

The local and/or a “global” compression of the region of low density canbe an elastic compression or predominantly elastic compression. Thismeans, the compression relaxes (disappears) after removing themechanical load causing the compression or relaxes mostly. In otherwords: the second object provided can be elastically deformable. Theapplicability of the bonding method also to second objects that areelastically compressible is an important advantage over known bondingmethods that base on hard, this means not compressible, objects or onobjects including portions that deform plastically, this meansirreversible, only, for example hollow core boards (HCB).

Hence, a surface or region of low density means in many embodiment notonly a surface or region that is at least one of porous, fibrous andsoft and/or that it includes a plurality of structures, voids, openingsetc., but also a surface or region that is compressible, in particularelastically compressible. Further, the surface or region can be locallycompressible, this means compressible in a way that it can includeregions that are compressed differently.

The compression can lead to an increase in compressive strength.

In embodiments, the second object may consist of a second objectcomposition and the structures of the second object may be formedinherently by the composition. For example, the structures can be pores,voids, channels etc.

For example, the second object can include or consist of fibers,textiles, foam, porous materials, cardboard etc. It can be formed by asequence of layers, wherein some of the layers can be at least one ofrigid, non-compressible, dense (this means a low concentration of pores,voids, channels, etc.), and load-bearing. The second object and/orlayers that form the second object can have a composition that isposition dependent. In addition or alternatively, the sequence of layerscan be position dependent.

In particular in embodiments of the method resulting in the protrudingportion after the step of letting the thermoplastic material resolidify,the structures are such that a deep-effective anchoring, this means ananchoring in the volume of the second object and not only on itssurface, is possible. However, one can envisage embodiments in whichthere is no need for specific structures for deep-effective anchoring.The embodiment including a proximal top layer as described below orembodiments aiming for the attachment of a third object as describedbelow, wherein the third object guarantees that the protruding portionprotrudes at least partly into the region of low density are example ofsuch embodiments.

In addition or alternatively, one can also envisage to generate thestructures of the second object, for example by roughening surfaces ofthe second object and/or by using a production process for the secondobject that generates such structures.

The mechanical excitation can set in after, prior to or at the same timeof applying the mechanical pressing force. A mechanical pressing forcethat sets in prior to the mechanical excitation can be favourable interms of bonding quality, in particular in terms of bonding depth andstrength of the bonding generated. However, one can envisageconfiguration in which the mechanical excitation can help to optimizethe penetration behaviour of the protrusion(s). Some of theseconfigurations are discussed below.

The mechanical pressing force can last for a time sufficient forresolidification of the thermoplastic material after stopping themechanical excitation.

The mechanical pressing force can vary during the step of applying themechanical pressing force and the mechanical excitation and—as the casemay be—during resolidification of the thermoplastic material.

The thermoplastic material of the first object is capable of being madeflowable by absorption of the mechanical energy generated by themechanical excitation, in particular mechanical oscillations/vibrationswhile the objects are pressed against each other. For example, themechanical vibration energy can be coupled through the first and/orsecond object to an interface generated by thermoplastic material of thefirst object and material of the second object. At the interface,external and possibly also internal friction will cause thermoplasticmaterial to heat and become flowable. Flowable thermoplastic materialwill then be pressed into the structures of the second object due to thepressure applied.

Portions of the first and/or second object that form the interface caninclude a profile that may serve as energy director, i.e., the energyabsorption and heat generation will automatically be focussed on oraround the respective interface.

In an embodiment, the second object provided includes a density profilethat increases as a function of the distance from the proximal surface.In particular, the density increases in a distal direction normal to theproximal surface.

The increase in density can be continuous or stepwise.

If the second object extends between the proximal surface and a distalsurface, the density can increase over a limited range of the secondobject, only.

The region of low density can be located at the proximal surface, theregion of low density can be located at the distal surface, or theregion of low density can be located somewhere between the proximal andthe distal surface.

One can also envisage a second region of low density, one located at theproximal surface and the other one located at the distal surface, forexample.

In an embodiment, the second object includes the region of low densitylocated at the proximal surface (i.e. the region of low density is aproximal region) and a further region of high density located distallyof the region of low density.

The region of low density is then a region having a lower density thanthe region of high density (i.e. than the further region).

The term “high density” in the region of high density or a region ofhigh density is used to express the density of the region relative tothe density of another region, in particular the region of low density.However, this term does not necessarily mean that the region of “highdensity” does not include a plurality of structures, voids, openings,etc. It does also not mean that the region is not compressible or thatthere is no need to compress the region to generate a critical densityand/or compressive strength (details below). Rather, the region can haveall physical properties attributed to a region of low density, too.However, the second object includes at least one region that has a lowerdensity than the region of “high density”.

In another embodiment, the further region is arranged distally of theregion of low density, wherein the region of low density is not locatedat the proximal surface.

Alternatively or in addition to the further region, the region of lowdensity can have a density that increases as a function of the distancefrom the proximal surface.

In an embodiment, the second object provided includes a proximal toplayer, wherein the region of low density is arranged distally of theproximal top layer, and wherein the method includes the step of forcingthe protrusion through the proximal top layer before liquefaction of thethermoplastic material.

The proximal top layer can be an integral part of the second object, forexample the cover layer in “hollow core”-like board, wherein the regionof low density fills the core region at least partly, or a cover layer,such as a decorative and/or functional cover layer, for example made of(artificial) leather, or any other external cladding.

The proximal top layer can be provided in a further step of the methodand be positioned on the proximal surface of the second object in yet afurther step of the method. In particular, the proximal top layer can bea third object as described below, for example a metal sheet, a foil ora cover layer. However, it can also be a cover layer or cladding asmentioned above, for example.

The density of the proximal top layer is higher than the density of theregion of low density, generally.

The proximal top layer can be the further region of high density.

The proximal top layer can contribute to any density profile of thesecond object discussed above or it can be in addition to such a densityprofile.

In particular, it can be in addition to any density profile of theregion of low density and—if present—of the further region.

One can envisage configurations in which there is no need for a regionof high density. For example, a mechanical pressing force can be appliedsuch that the distal end penetrates the region of low density partly, ina first step. In a subsequent second step, the mechanical oscillationscan be applied with such an amplitude that the thermoplastic materialbecomes flowable. In addition, the mechanical pressing force can bereduced in order to reduce the velocity with which the first objectpenetrates the second object.

Alternatively or in addition, the proximal top layer or any other layerarranged proximally of the region of low density can cause a warming ofthe thermoplastic material when the protrusion is pushed through thelayer. The warming is not sufficient to liquefy the thermoplasticmaterial, but it reduces the mechanical pressing force and themechanical excitation needed in the step of applying a mechanicalpressing force and a mechanical excitation capable to liquefy thethermoplastic material.

In embodiments including a second object with any density profile asdescribed above and, as the case may be, including the proximal toplayer, the distal end of the first object (often the protrusion(s))penetrates the region of low density at least partly before thethermoplastic material is made flowable.

The density profile can be such that the density of the second object inthe region of low density is not high enough to generate the pressureneeded to liquefy the thermoplastic material. In particular, the densityin the region of low density is not high enough to cause liquefaction ofthe thermoplastic material when the mechanical pressing force and themechanical excitation is applied for less than 15 s or less than 10 s,for example less than 5 s or 2 s. In particular, the density is not highenough to cause liquefaction when the mechanical pressing force and themechanical excitation is applied for 0.1 to 1 s, for example for 0.1 to0.5 s.

Alternatively or in addition, the step of applying the mechanicalexcitation needed to liquefy the thermoplastic material sets in afterpenetration of the distal end of the first object through the region oflow density.

In an embodiment that is applicable to any density profile of the secondobject and/or the region of low density, the method includes the step ofcompressing the region of low density at least locally such that acritical density needed for the liquefaction of the thermoplasticmaterial is generated.

The critical density corresponds to the density at which the criticalcompressive strength is established.

The step of compressing the region of low density at least locally canbe a substep of the step of applying the mechanical pressing force andthe mechanical excitation capable to liquefy the thermoplastic material.

In particular, the step of compressing the region of low density atleast locally to a critical density can be prior to the step of applyingthe mechanical excitation.

The critical density that needs to be established depends on the aimedduration of applying the mechanical pressing force and the mechanicalexcitation after which liquefaction should occur.

The compression can be a global compression and/or a local compression.

The global compression can be established by compressing the region oflow density over a wider area and not only around the protrusion(s). Forexample, this can be done by the first object body, in particular by itsdistal surface or by a portion of it. In particular, the first objectbody can penetrate into the region of low density at least partly.

Alternatively, the global compression can be established in the same wayby another object that is attached to the second object by the use ofthe first object.

The local compression can be established by the protrusion(s), forexample by displacing the portion(s) of the region of low density intowhich the protrusion(s) are forced.

Experiments have shown that in particular incoherent materials, such aspanels made from a fibrous material, show a surprising stress-strainbehaviour when a force (load) is applied locally to such a material.“Locally” in this context means that the force (load) is applied to anarea of an item formed by the incoherent material, the area beingsignificantly smaller that a corresponding extension of the item.

The following behaviour has been found on a variety of items ofincoherent materials when a pressing force is applied locally and normalto the item:

-   -   An approximately linear dependence of the stress on strain can        be observed as soon as strain is applied to the item. The        roughly linear dependence forms a first region of linear        dependence. The linear dependence of the stress on strain in the        first region can be approximated by a straight line having a        first slope.    -   A transition region in which the dependence of stress on strain        increases steadily follows the first region of linear dependence        when strain is further increased.    -   A second region of approximately linear dependency of stress on        strain follows the transition region when strain is even further        increased. The roughly linear dependence of the stress on strain        in the second region can be approximated by a straight line        having a second slope, wherein the second slope is larger than        the first slope.

The pressing force (load) was applied by an intender having a relevantsurface area between 4 and 200 mm². However, there is no hint that thebehaviour summarized above is restricted to this range of relevantsurface areas.

Due to this behaviour, a broad range of incoherent materials aresurprisingly suitable for use in bonding methods relying on theliquefaction of thermoplastic material by the use of a mechanicalpressing force and a mechanical excitation, in particular vibrations.This is because a broad range of incoherent materials reach the stresslevel needed for liquefaction of the thermoplastic material, i.e., thecritical compressive strength, due to the existence of the second regionof linear dependency, only.

Hence, the step of compressing the region of low density can be suchthat the stress-strain behaviour of the material is in the second regionof linear dependency.

The strain value at which the first and second slope cross in thestress-strain diagram is a characteristic value of the stress-strainbehaviour observed.

The step of compressing the region of low density can be such that thematerial is compressed to the characteristic value, at least.

Alternatively or in addition, the characteristic value can define alower threshold for applying, this means switching on, the mechanicalexcitation used in the step of applying the mechanical pressing forceand the mechanical excitation capable to liquefy the thermoplasticmaterial. In other words, the mechanical excitation can be switched onat an applied pressing force that causes the characteristic strainvalue.

Further, it has been observed that deformation of the panels is largelyreversible as long as liquefied thermoplastic material that has beenpressed into pores, openings, etc., of the panel does not prevent thepanel from returning to its original shape.

However, there can be configurations in which the deformation of theregion of low density is irreversible, for example if the energy coupledinto the panel is high enough to cause a permanent densification. Forexample, the region of low density can include fibers that melt duringthe method.

Any permanent deformation can be advantageous in terms of bondingstrength.

In particular with incoherent materials, the critical density can beestablished around the protrusion(s) only, for example by a localincrease of the global compression by an amount sufficient to reach thecritical density.

Regions of the second object different from the region of low densityand/or the proximal top layer and/or at least a portion of any object(e.g., a third object, a cover layer, an external cladding) to beattached or attached to the second object can be compressible, too.Hence, these regions and/or objects can contribute to a density profilethat is in favour for liquefaction of the thermoplastic material andthat is established during the method of bonding the first object to thesecond object. In particular, liquefaction can take place in suchregions and/or objects, too.

In addition, the distal end of the first object, in particular theprotrusion(s), can include a structure designed and arranged to promotelocal compression of the second object when it is forced into the secondobject. In particular, it is the region of low density that iscompressed at least locally when the structure is forced into the regionof low density.

Forcing the first object into the second object can be done in a furtherstep including a movement, in particular a (partly) penetratingmovement, of the first object relative to the second object. Generally,the local compression is an effect generated by the design andarrangement of the structure and by the relative movement.

The structures designed and arranged to promote local compression canhave at least one of the following effects besides the effect ofcompressing the region of low density locally (in other words ofincreasing the density locally):

-   -   Material of the second object, for example fibers, is pulled in        distal direction when the first object is pushed into the region        of low density. This can lead to the additional effect of        felting, in particular if the second object includes fibers.    -   Material of the second object is embedded in the structures and        hence in the protrusion(s). This leads to a more even        distribution of load acting on the bonded first and second        object in use.        -   The quality of the embedment can be increased if the second            object includes thermoplastic material such that a weld is            formed between the structure or the protrusion in general            and the second object and/or such that the second object            changes is structural properties. Embodiments including a            weld are described in detail below.

For example, the first object can include at least one barb, for examplea barb in the shape of a catching barb and/or a drag down barb. The barbcan be significantly smaller than the protrusion or it can have a sizesuch that the barb contributes to the overall shape of the protrusion.In the latter case, the cross-section of the protrusion in a planeperpendicular to a longitudinal axis of the protrusion (also calledprotrusion axis) can depend significantly on the shape of the barband/or it can depend on the position of the plane due to the presence ofthe barb, for example.

Multiple tips arranged with or without offset along the protrusion axisare further examples of structure designed and arranged to promote localcompression

Such a barb or the structure in general can be arranged to increase thedensity faced by the penetrating distal end, for example by collectingfibers. In other words: the barb makes sure that the density in front ofthe distal end increases in dependence of the penetration depth of thedistal end into the second object.

Such a barb can also be present in embodiment, in which the secondobject includes an increasing density profile.

In addition to a compression of the region of low density, a weld can beformed between the thermoplastic material and a compressed regionsurrounding the protrusion(s) by choosing the material of the region oflow density accordingly.

Embodiments in which a weld is formed are described in detail below. Forexample, the region of low density can include thermoplastic fibers.

An advantage of the embodiment including the compression of the regionof low density is that the region does not need to have a density neededto liquefy the thermoplastic material generally or at a specificposition. Rather, the density can be low and/or homogeneous. As pointedout above, the needed density or density profile can be generated duringthe process of bonding the first object to the second object.

Independent of the exact density profile of the second object, thedistal end or a portion of the distal end, for example at least one of aplurality of protrusion, can penetrate the second object from theproximal to the distal end. Bonding of the first object to the secondobject can then be established by the use of an anvil including aproximal surface with a head-forming recess. In this embodiment, themethod includes the step of positioning the proximal surface of theanvil relative to the distal end of the second object such that thepenetrating distal end of the first object enters the head-formingrecess.

Examples of second objects having a region of low density, for exampleat a surface, and—as the case may be—an increasing density in adirection normal to the surface are panels, insulations, sheathings,fairings, trims, carriers, absorbers, and decors used in vehicles, suchas automobiles, trains and planes, for example in the luggagecompartment, in the interior of the vehicle or around a wheelhouse.

For example, the second object can include natural or synthetic fibers,for example cotton or polyester fibers. These fibers can be embedded ina plastic, in particular a thermoplastic material, wherein free ends ofthe fibers, this means portions of the fibers not embedded in theplastic, form the region of low density. The arrangement of fibers andplastic can be such that the density increases continuously startingfrom the proximal surface and—optionally—decreases again towards thedistal surface. However, the arrangement of fibers and plastic can besuch that the density is essentially constant in the region formed bythe free ends of the fibers, i.e., in the region of low density and/orthat the density is essentially constant in the region formed by thefibers embedded in the plastic. In particular, there can be anessentially step-like increase in density when entering the regionformed by the fibers embedded in the plastic.

Another group of second objects including somewhere, in particular at orclose to the proximal surface, an increase in density in a directionnormal to its surface are panels, sheathings, fairings, trims andcarriers including a functional layer attached to a core. For example,the functional layer can be at least one of soft, softening, damping andcurbing, in particular by including a plurality of openings, voids,movable components and/or non-rigid components.

Another example are dashboards including a top layer, for example a toplayer made of artificial leather, that is arranged on a foam, whereinthe foam becomes more dense and rigid with increasing distance from thetop layer. Such dashboards can be considered as examples of a secondobject including a proximal top layer, wherein the region of low densityis arranged distally of the proximal top layer.

In a group of embodiments, the first object includes an element of aconnecting device, such as a thread, a cable holder, an element of asnap lock or of a bayonet lock.

In embodiments, the first object is a connector. In particular, thefirst object can form or be the element of a connecting device.

In an embodiment, the method further includes the step of providing afurther object including an attachment location adapted to the elementof the connecting device and the step of connecting the bonded first andsecond object to the further object.

In particular, the further object can be the device to which the secondobject, e.g., the panel, sheathing, fairing, trim or carrier has to bemounted.

The attachment location can be a counterpart of the element of theconnecting device comprised or formed by the first object.

In an embodiment, the method includes the step of providing the furtherobject and the first object includes a first object body that isdesigned to form a connection with a further object. The first objectbody can be according to any one of the embodiments described below.

The further object can be a fixing element such as a nail, a screw, arivet, etc.

The further object can be equipped to mount an object different from thefirst, second and further object to the first and/or second object.

In particular, the further object provided can include a distal end, forexample a tapered distal end, and the connection between the firstobject body and the further object is generated by the distal end of thefurther object penetrating the first object body at least partly.

The method can include the further steps of positioning the distal endof the further object relative to the first object body and of applyinga mechanical pressing force to at least one of the first, second orfurther object, wherein the mechanical pressing force is such that thedistal end of the further object penetrates the first object body atleast partly.

In particular, the further steps are performed after the step ofstopping the mechanical excitation and letting the thermoplasticmaterial resolidify, this means after bonding the first object to thesecond object.

For example, the first object can be a reinforcement element. Such areinforcement element has the effect to increase the mechanicalstability of the second object after being bonded to the second object.In other words: The first object is designed to reinforce the secondobject locally such that a reliable connection between the furtherobject and the second object via the first object can be established.

The use of the first object as a reinforcement element is advantageousin particular when the density profile of the second object does notallow for a specific connection, for example a connection based onnails, screws, rivets etc., and/or the mechanical stability of thesecond object is such that various connection methods cannot be used forreliable connection, for example due to the second object beingbendable. Connections based on nails, screws, rivets, but also methodsbased on adhesives are examples of connections that do not result in areliable connection between the further object and the second object ifthe second object is bendable, for example.

In addition or alternatively, the connection between the first objectbody and the further object can be generated by the first object bodyincluding an element of a connection device as described above and bythe further object including a related counter-element.

An important advantage of connecting and/or attaching an objectdifferent from the first and second object to the second object by theuse of the first object acting as a connection location (i.e. by using atwo-step process) is that the object can be removed again. Thisstatement is true independent of the concrete realization of theconnection and/or attachment. In particular, the first object caninclude an element of a connecting device or the first object body canbe designed to form the connection.

In an embodiment, the first object body includes a proximal surface, adistal surface and a connection location. The connection locationincludes at least a portion of the proximal surface of the first objectbody. For example, the connection location or a part of it extends as aprotrusion from the proximal surface portion or the connection locationor a part of it is an opening in the first object body, wherein theproximal surface portion forms a mouth of the opening.

In this embodiment, the first object includes a protrusion region, inparticular a protrusion region in any one of the embodiments describedbelow, arranged at the distal surface of the first object body and afunctional region, in particular a functional region in any one of theembodiments described below, that does not include any protrusions,wherein the functional region is opposite of the proximal surfaceportion comprised by the connection location.

In embodiments, the mechanical pressing force and the mechanicalexcitation are applied locally to the at least one of the first andsecond object. In other words, the first object is bonded to the secondobject at bonding locations that are separate from each other, i.e., thebonding is generated by the use of bonding points and not by acontinuous extensive bonding area.

For example, the bonding locations can be round, elliptic, rectangularor square having a characteristic length that is significantly smallerthan a characteristic extension over which the first and second objectare to be bonded together. In particular, the characteristic length isbetween a few millimeters to a few centimeters, for example between 1 mmand 10 cm, in particular between 1 mm and 5 cm, for example 0.5 mm, 1cm, 2 cm, 3 cm, 4 cm or 5 cm. However, one can envisage situations inwhich a characteristic length of more than 10 cm are needed, for exampleif the first object forms a closed or partly closed form with a centralopening.

In such embodiments, the step of applying the mechanical pressing forceand the mechanical excitation and the step of stopping the mechanicalexcitation and letting the thermoplastic material resolidify is repeatedseveral times at different positions on at least one of the first orsecond object.

It is an advantage of this embodiment that there is no limitationconcerning the shape of the first and second object as long as they canbe arranged to form an assembly of the first and second object includingbonding locations and as long as these locations are accessible for atool used to apply the mechanical pressing force and the mechanicalexcitation.

In particular, there is no need that the first and/or second objectis/are essentially flat. Rather, one or both of the objects can becurved. Further, there is no restriction concerning the position of thebonding location with respect to each. For example, there is no needthat the bonding location are arranged on plane or on planes that runparallel to each other.

An example of a tool equipped to apply the mechanical pressing force andthe mechanical excitation is a handheld sonotrode or a sonotrode mountedon a robot arm.

The number of times the step of applying the mechanical pressing forceand the mechanical excitation and the step of stopping the mechanicalexcitation and letting the thermoplastic material resolidify is repeateddepends on various parameters such as the shape and the material of thefirst and second object and the strength of the bond needed.

In embodiments, the axis along which the mechanical oscillations occur,is essentially perpendicular to the proximal surface.

In the case of separate bonding locations, the axis along which themechanical oscillations occur, is essentially perpendicular to theportion of the proximal surface defining the bonding location.

The proximal end of the first object can include a coupling-in faceequipped for receiving the mechanical pressure force and the mechanicalexcitation. The coupling-in face after the step of arranging the firstand the second object relative to each other such that an assembly ofthe first and second object is formed can be arranged parallel to theproximal surface or the portion of the proximal surface defining thebonding location.

In an embodiment, the first object provided includes the coupling-inface and the method further includes the steps of providing a sonotrodeincluding a coupling-out face adapted to the coupling-in face and ofbringing the coupling-out face in contact with the coupling-in faceprior to the step of applying the mechanical pressing force.

Alternatively, the second object, in particular a distal surface of thesecond object can include the coupling-in face. In other words: Themechanical pressing force and the mechanical excitation needed toliquefy the thermoplastic material can be applied to the distal surfaceof the second object.

In an embodiment, the first object, the second object and the sonotrodecan be arranged relative to each other such that the second object isbetween the first object and the sonotrode and such that the proximalsurface of the second object is in contact with the at least oneprotrusion or gets in contact with the at least one protrusion of thefirst object during the method.

For example, the first object can be formed by a part of a car body onwhich the at least one protrusion including the thermoplastic materialis arranged. The second object can be a cover. The shape of the covercan be adapted to the shape of the car body and/or the arrangement ofthe first object(s). According to this exemplary embodiment, the secondobject is positioned on the first object and the sonotrode is applied onsurface regions of the second object that are opposite to surfaceregions of the second object that are in contact with a protrusion.

The mechanical pressing force and the mechanical excitation can beapplied to the distal surface of the second object by use of thesonotrode. In this embodiment of the method, the distal surface of thesecond object is an exposed, “proximal” surface for a user that operatesthe sonotrode due to the fact that the surfaces of the objects aredefined relative to an origin in the middle of the first object.

In embodiments in which the sonotrode is applied to the second object,the method can include a step of compressing the second object, forexample the step of compressing the region of low density. Inparticular, the compression can be such that the second object becomescapable to transmit the mechanical excitation applied to the distalsurface of the second object.

The surprising stress-strain behaviour discussed above make a broadrange of incoherent materials suitable for transmitting the mechanicalexcitation used in bonding methods relying on the liquefaction ofthermoplastic material by the use of a mechanical pressing force andmechanical excitation, in particular vibrations. Again, this is becausea broad range of incoherent materials reach the stress level needed fortransmitting the mechanical excitation thanks to the existence of thesecond region of linear dependency, only.

Hence, the step of compressing the region of low density can be suchthat the stress-strain behaviour of the material is in the second regionof linear dependency and/or such that the material is compressed to thecharacteristic strain-value given by the crossing of the first andsecond slope.

In embodiments in which the sonotrode is applied to the first object,the step of applying the mechanical pressing force and the mechanicalexcitation to the first/second object can be done by the sonotrode beingpressed against the coupling-in face of the first object while thesecond object may be optionally held directly or indirectly by a support(that may be held directly against the second object at the lateralposition at which the sonotrode acts, or that may be constituted by aframework of a more complex object that holds the second object; suchcomplex framework may, for example, be a body of an item to beassembled, such as a car body).

Optionally, the method can further include the step of locking the firstobject to the sonotrode after the step of bringing the coupling-out facein contact with the coupling-in face.

A distal end of the sonotrode including the coupling-out face caninclude openings and recesses such that a proximal protrusion of thefirst object is unaffected by the use of the sonotrode.

The mentioned element of a connecting device is an example of a possibleproximal protrusion of the first object.

The sonotrode can be a ring-sonotrode.

The distal end of the sonotrode, in particular the coupling-out face,and the extension of the first object, in particular the extension ofthe first object at its proximal end, for example the coupling-in face,can be such that the distal end of the sonotrode covers at least theproximal end of the first object during bonding.

However, it is also possible that the distal end of the sonotrode andthe extension of the first object are such that the mechanical pressingforce and the mechanical oscillations applied to the first object by thesonotrode are local, only.

One can also envisage to apply the mechanical pressing force and themechanical excitation to a plurality of bonding locationssimultaneously. For example, this can be done by a sonotrode including adistal coupling face that is adapted to the bonding locations to beestablished.

In an embodiment, the first object provided includes a protrusion regiondistally of the first object body, wherein the first object bodyincludes a distal surface and wherein the protrusion region includes aplurality of protrusions that includes the thermoplastic material.

One can envisage that not all protrusions, but a multitude ofprotrusions for example, include a protruding portion after the step ofstopping the mechanical excitation and letting the thermoplasticmaterial resolidify.

Each protrusion includes an extension in distal direction and athickness. For example, the extension in distal direction is the lengthof the protrusion if the longitudinal protrusion axis runs along theaxis perpendicular to the distal surface.

The extension of the protrusions in distal direction can vary within theplurality of protrusions comprised in the protrusion region.

In particular, the first object can include at least one protrusion of afirst kind including the thermoplastic material and at least oneprotrusion of a second kind including the thermoplastic material,wherein the extension in distal direction of the protrusion of the firstkind is larger than the corresponding extension in distal direction ofthe protrusion of the second kind. Hence, the positive-fit connectionestablished by the protrusion of the first kind is at a different distalposition than the positive-fit connection established by the protrusionof the second kind.

Embodiments including a protrusion of the first kind and a protrusion ofthe second kind (and, as the case may be, protrusions of further kinds,this means of protrusions having an extension in distal direction thatis different form the extension in distal direction of the protrusion ofthe first kind, the second kind and of each other) can include at leastone of:

-   -   Extensions in distal direction of the protrusions are chosen        such that the bonding of the first object to the second object        is established by involving a larger volume of the second object        compared to the bonding based on extensions with equal extension        in distal direction.    -   Protrusions with large or larger extension in distal direction        and with small or smaller extension in distal direction are        arranged such that a subsequent processing step, for example a        forming step, of an item including the first object that is        bonded to the second object is possible.    -   Protrusions with large or larger extension in distal direction        and with small or smaller extension in distal direction are        arranged such that a bending strength and/or tension strength is        optimized.        -   For example, protrusions with a large extension can be            arranged on the distal surface next to a lateral edge or            lateral edges of the first object body, wherein protrusions            with a smaller extension can be arranged at the center of            the distal surface of the first object body.    -   Protrusions with different extensions in distal direction that        are optimized in terms of material costs, optionally in        combination with an arrangement of the protrusions with        different extensions in distal direction that is optimized for a        specific application and the pulling/bending forces accompanied        by the application.

Independent of the concrete embodiment of the method or the device (thismeans the first object), the protruding portion corresponds to therelated protrusion after its deformation during the step of stopping themechanical excitation and letting the thermoplastic material resolidify.Hence, it is located in the region of the initial protrusion withrespect to the first object body. In particular, the protruding portionprotrudes at the same position from the distal surface of the firstobject as the protrusion before applying the mechanical pressing forceand the mechanical excitation.

For example, the protruding portion can be a portion of the protrusionthat does not liquefy during the step of applying the mechanicalpressing force and the mechanical excitation. However, the protrudingportion can also be an accumulation of re-solidified material in aregion relative to the first object at which a protrusion has beenpresent before the step of applying the mechanical pressing force andthe mechanical excitation.

An effect of protruding portion(s) after the step of stopping themechanical excitation and letting the thermoplastic material resolidifyis a bonding area that extends into the second object, this means thatis not restricted to the surface area of the second object, only. Inother words: a deep-effective anchorage is established. This increasesthe mechanical strength of the bond, in particular its mechanical loadcapability, significantly compared to bonds without protruding portions.

The protrusion(s) used in embodiments of the invention are not energydirectors as described below. For example, the protrusion(s) aredimensioned along the axis perpendicular to the distal surface of thefirst object body such that they allow for deep-effective anchorage.This means that their extension along the axis perpendicular to thedistal surface is larger than the corresponding extension of energydirectors. Further, the protrusion(s) can form the protruding portionafter the step of stopping the mechanical excitation and letting thethermoplastic material resolidify. Energy directors do not form suchprotruding portions because they define positions at which liquefactionsets in which also means that they disperse during the step of applyingthe mechanical pressing force and the mechanical excitation.

However, the protrusion(s) can include energy directors.

The protrusion(s) can be tapered and have any pointed and/or sharp form,such as a ridge or a tip, for example.

The protrusion(s) can also diminish in diameter in step-like manner orthey can be constant in diameter

The protrusion, some protrusions or all protrusions can include thestructure designed and arranged to promote local compression mentionedabove.

The protrusion or at least one of the protrusions can be asymmetric inshape. In particular, it can have a shape that is not rotation-symmetricwith respect to an axis perpendicular to the distal surface of the firstobject body.

In an embodiment, the protrusion or at least one of the protrusions isat least one of:

-   -   Equipped for defining a deformation direction during the step of        applying the mechanical pressing force and the mechanical        excitation.        -   For example, the protrusion can include a recess arranged            such that the protrusion deforms in a specific direction            when loaded and/or the protrusion can be bent away from the            axis perpendicular to the distal surface of the first object            body before the step of applying the mechanical pressing            force and the mechanical excitation.    -   Equipped for defining a direction into which liquefied        thermoplastic material flows during the step of applying the        mechanical pressing force and the mechanical excitation, and    -   Including a protrusion axis that runs at an angle to the distal        surface of the first object body, wherein the angle is not a        right angle.

Each protrusion includes an extension in distal direction and athickness, as mentioned above. The extension in distal direction is thelength of the protrusion if a longitudinal protrusion axis runs alongthe axis perpendicular to the distal surface.

In an embodiment, the ratio between the extension in distal directionand the thickness is at least 1, in particular between 1 and 5, forexample between 1.5 and 4 or between 2 and 3. In other words: theextension of the protrusion(s) along the axis perpendicular to thedistal surfaces is larger than a thickness along a direction that isradial to the perpendicular axis.

In embodiments, the extension in distal direction of the protrusion(s)corresponds to 10%-80% of the corresponding thickness of the secondobject or—depending on the concrete realization of the second object—to10%-80% of the corresponding thickness of the region of low density. Inparticular, the extension in distal direction of the protrusion(s)corresponds to 15%-70% or to 20%-50% of the corresponding thickness.

In embodiments including a plurality of protrusions, the protrusionregion includes gaps between the protrusions.

Within this text, “gaps” means the overall space separating a protrusionfrom other protrusions rather than a distance between protrusions.

The gaps can extend to the distal surface of the first object body. Inparticular, the protrusions can be arranged on the distal surface of thefirst object body in a manner that flat regions of the distal surfaceare formed between the protrusions.

The flat regions can form stopping surfaces as described below.

As mentioned above, the surfaces of the first object defining the gapscan be arranged to compress the first object, in particular the regionof low density, prior to liquefying the thermoplastic material.

In particular, the surfaces are arranged such that a global compressionand an additional local compression results, wherein the localcompression occurs around the protrusion and guarantees the criticalcompression needed for liquefaction of the thermoplastic material.

Further, the surfaces effect a stabilization of the bonding process dueto the fact that a steadily increasing counterforce to the appliedmechanical pressing force is generated. This also helps avoiding anunintentional piercing of the second object or the region of low densityand compensating for density variations in the second object or theregion of low density.

The total volume of the protrusion region can be given by the portion ofthe distal surface of the first object body including protrusions and anextension of the protrusion region in distal direction. For example, theextension of the protrusion region in distal direction can be theextension of the protrusions along the axis perpendicular to the distalsurface, wherein all protrusions have the same extension, and theportion of the distal surface including protrusions forms a base of theprotrusion region, such that the total volume of the protrusion regionis given by the product between the portion of the distal surface andthe extension.

In an embodiment, the total volume consists of the volume of theplurality of protrusions and of the volume of the gaps (this means thetotal volume of the space mentioned above) within the protrusion region,wherein the volume of the gaps is larger than the volume of theprotrusions. In other words: The ratio between the volume of the gapsand the volume of the protrusions is larger than 1, in particular largerthan 2, for example 3, 4, 5. In many embodiments, the ratio is smallerthan 10.

In an embodiment, the distal surface of the first object body includes afunctional region, this means a region that has a function differentfrom bonding the first and second object. Hence, the functional regiondoes not include any protrusions.

The functional region is not at all or only at the very end of thebonding in contact with the proximal surface of the second object.Therefore, its mechanical and/or thermal load is reduced significantlycompared to regions of the distal surface of the first object body thatinclude protrusions.

For example, the functional region includes a distal mouth of an openingthat goes through the first object body. The opening can be a guide fora wire or a sensor and/or it can form a finish of an opening in thesecond object, for example.

In embodiments the protrusions can consist of the thermoplastic materialor the thermoplastic material can be arranged at least partly around acore of a harder material. In this context, a harder material means amaterial that does not become flowable due to the mechanical pressureforce and mechanical excitation applied.

The harder material can be a plastic different from the thermoplasticmaterial or metallic, for example.

In particular, the tip or the part of the ridge of the protrusion(s)being in contact with the second object after arranging the first objectrelative to the second object can be made of harder material that is notcovered by the thermoplastic material.

Alternatively, at least one of the distal end of the protrusions, astep, and an edge can include the thermoplastic material. In suchembodiments, the protrusions form so-called energy directors by theirshape. This means, that they define one or more spots where theliquefaction of the thermoplastic material sets in.

Energy directors are structures at which the mechanical oscillationsand/or pressure force applied are focused and/or couple into thethermoplastic material in an efficient manner.

The first object in any embodiment can include energy directors thatdiffer from the energy directors possibly generated by the, for exampletapered, step-like or edgy, shape of the protrusions, for example byfurther tips and ridges that are arranged on the side of theprotrusions.

In embodiments in which the first object provided includes theprotrusions at its distal end, the method can include the step ofarranging the first object relative to the second object such that theprotrusions are in physical contact with the proximal surface.

In addition, the step of applying the mechanical pressing force caninclude applying a mechanical pressing force of a strength such that theprotrusions penetrate through the region of low density and otherregions optionally arranged proximally of the region of low density.

The effect of protruding the region of low density before applying apressure suitable for liquefaction of the thermoplastic material isgenerated and/or before applying the mechanical oscillations is abonding area that extends into the second object, i.e., which is notrestricted to the surface area of the second object, only.

This effect can be increased further by applying a mechanical pressingforce of a strength such that the protrusions penetrate into a region ofhigh density.

In particular, the step of applying the mechanical pressing forceincludes applying a first mechanical pressing force and a secondmechanical pressing force, wherein the first mechanical pressing forceis smaller than the second mechanical pressing force or equal to it.

For example, the first mechanical pressing force has a strength suchthat the distal end of the first object, for example the protrusions,penetrate the region of low density of the second object. The secondmechanical pressing force can have a strength such that the distal endof the first object, for example the protrusions, penetrate into theregion having a higher density.

The second mechanical pressing force can be adapted to guarantee awell-controlled penetration, e.g., in terms of penetration speed, intothe region having the higher density.

Generally, the second mechanical pressing force sets in prior to themechanical excitation capable to liquefy the thermoplastic material.

The increase from the first mechanical pressing force to the secondmechanical pressing force can be continuously or step-like.

In an embodiment, the method includes further the steps of:

-   -   providing a third object including a third object proximal        surface and a third object distal surface;    -   arranging the third object relative to the second object such        that the third object distal surface is in physical contact with        the proximal surface of the second object;    -   forcing at least a portion of the first object through the third        object from its proximal surface to its distal surface prior to        the step of applying the mechanical excitation capable to        liquefy the thermoplastic material and to cause the flowable        portion of the thermoplastic material to penetrate into the        structures of the second object.

However, it is a further insight of the invention that bothprotrusion(s) including the thermoplastic material in a solid state andprotrusion(s) consisting of the thermoplastic material can be used topierce third objects of various materials and dimensions by optimizingthe mechanical pressing force, the mechanical excitation and the onsetof the mechanical excitation relative to the onset of the mechanicalpressing force.

In an embodiment, the third object can include or consist of a sheetmaterial without pre-drilled bores and the method can include the stepof piercing the sheet material before the mechanical pressing force andthe mechanical excitation capable to liquefy the thermoplastic materialis applied. However, this does not imply that no mechanical pressingforce and/or mechanical excitation is applied during the step ofpiercing the metal sheet.

The sheet material to be pierced can be a flange arranged to fix thethird object to the second object.

The sheet material can be arranged relative to the first and secondobject such that a first protrusion of the first object pierces thesheet material before bonding the first object to the second object andsuch that a second protrusion does not get in contact with the sheetmaterial during the method.

In particular, the sheet material can be a metal sheet.

Experiments have shown that piercing of titanium sheets of a thickness(strength) of up to 0.3 mm and aluminium sheets of a thickness of up to0.5 mm can be pierced, at least.

In an embodiment with or without providing a third object, the methodcan include a step of using the mechanical excitation to adjust thepenetration behaviour of the protrusion(s).

If the mechanical excitation used in combination with a pressure actingon the thermoplastic material that is not capable to liquefy thethermoplastic material, the penetration depth of the protrusion(s) intothe second object can be adjusted.

If the mechanical excitation used in combination with the pressureacting on the thermoplastic material is capable to liquefy thethermoplastic material, the thermoplastic material can be liquefied andpressed into the second object in a continuous manner. This can lead toa layer-like region in the second object or a head-like structure on thedistal surface of the second object and hence to a more reliable bond.

Additionally, the method according to this embodiment can include thestep of compressing portions of the second object locally and/orglobally to reach the critical density needed to liquefaction of thethermoplastic material.

In an embodiment, the first object includes at least one protrusion of afirst kind including the thermoplastic material and at least oneprotrusion of the second kind including the thermoplastic material. Theshape of the protrusion of the first kind can be such that the flowableportion of the thermoplastic material penetrates into the structures ofthe second object and the shape of the protrusion of the second kind issuch that a flowable portion of the thermoplastic material penetratesinto structures of the third object during the step of applying themechanical pressing force and the mechanical excitation capable toliquefy the thermoplastic material.

For example, the dimensions, in particular the length and thickness, ofthe protrusion of the first kind and the dimensions of the protrusion ofthe second kind can be adapted to each other and to the thickness of thesecond and third object, such that their liquefaction sets in at thedesired positions in second and third object, respectively.

In particular, the third object can have the same density profile as thesecond object. In this case, the length of the protrusion of the firstkind and the length of the protrusion of the second kind can be adaptedto the distance of the regions of low density from the proximal surfaceof the third object.

A depth of the bonding area in the second object can be adjusted by thetime duration of the mechanical pressing force applied prior to applyingthe mechanical excitation and/or the strength of the mechanical pressingforce.

The first object provided can include a mark indicating the penetrationdepth of the first object into the second object prior to the step ofapplying both the mechanical pressing force and the mechanicalexcitation capable to liquefy the thermoplastic material.

The depth of the bonding area in the second object corresponds to amaximum penetration depth of the thermoplastic material of the firstobject into the second object after resolidification. The maximumpenetration depth is measured along the axis along which the firstobject is forced into the second object.

Often, the maximum penetration depth is measured along an axis normal tothe proximal surface of the second object or—as the case may be—normalto the portion of the proximal surface defining the bonding location.

In embodiments, the step of applying mechanical pressure may be carriedout until abutting surface portions of the first and second objects (orthe first and third object, as the case may be) lie against each other.

In particular, a first object including a stopping surface is provided.For example, the stopping surface is a surface arranged to lie flatly onthe second (third) object after bonding the first object to the secondobject.

Such a stopping surface can define a maximum penetration depth of thethermoplastic material of the first object into the second object.

If the first object includes a protrusion, the protrusion protrudesdistally from the stopping surface.

If the first object includes the mark indicating the penetration depthof the first object into the second object prior to liquefaction of thefirst object, the stopping surface is arranged proximally of the mark.

Measures that have the effect of a well-defined depth of the bondingarea are advantageous in the case of a second object including a distalsurface that has to be unaffected by the method of bonding the firstobject to the second object.

A decorative layer, a so-called “A-surface” or any other surface that isvisible for the user after bonding are examples of surfaces that have tobe unaffected by the bonding method.

In an embodiment, the method further includes the steps of providing thethird object including the third object proximal surface and the thirdobject distal surface, arranging the third object relative to the secondobject such that at least a portion of the third object distal surfaceis in physical contact with the proximal surface of the second object,and forcing at least a portion of the protrusion through the thirdobject from its proximal face to its distal face.

In such embodiments, the third object is in particular at least one of:

-   -   A metal sheet including a through bore. The through bore can        form a region that is bent in the distal direction.        -   The bent region can lead to a local compression of the            second object during a step of pressing the bent region into            the second object.        -   The trough bore is designed such that there is a protruding            portion in the second object after bonding the first object            to the second object, this means after attaching the third            object to the second object by bonding the first object to            the second object. This also means that the protrusion can            lead to a (further, as the case may be) local compression of            the second object in the region of the opening.        -   The method can include the further step of applying a            lateral compressing force to a portion of the protrusion and            to generate a melting zone at a contact surface between the            portion of the protrusion and the third object.        -   For example, the bent region can be elastically deformable            and the through bore that forms the bent region can have a            diameter that is smaller than a diameter of the protrusion.            Hence, the elastically deformable, bent region can be            deformed by pushing the protrusion through the opening. This            deformation can generate the lateral compressing force to            the portion of the protrusion.    -   A foil, wherein the foil is designed to be penetrable by the        protrusion. In particular, it can be provided as a perforated        foil. Alternatively, the foil can have a thickness and a        strength such that it can be penetrated by the protrusion during        the method.        -   Optionally, the foil can include or be made of a            thermoplastic material, such that a weld between the foil            and the protrusion can be formed.        -   One can envisage to provide a third object that is not a            foil and that is penetrable by the protrusion and/or            includes thermoplastic material, nevertheless.    -   A third object that includes a thickness and a density profile        such that the protrusion can penetrate the third object during        the step of applying the mechanical pressing force and the        mechanical excitation but without causing the thermoplastic        material of the protrusion to liquefy within or at a surface of        the third object.

Yet in another embodiment of the method including the further steps ofproviding the third object, the first object provided includes a firstobject body including the proximal surface of the first object body, thethird object provided includes the third object proximal surface and thethird object distal surface, and the method includes the further step ofarranging the third object relative to the first object such that thethird object distal surface is in physical contact with the proximalsurface of the first object body.

Optionally, the third object can be arranged and fixed on the firstobject such that the third object is not in direct contact with thesecond object.

The third object can be glued on the proximal surface of the firstobject body.

In an embodiment, the second object provided includes a distal surfaceand the first object provided as well as the step of applying themechanical pressing force and the mechanical excitation can be such thatthe distal surface is unaffected by the method.

In particular, the mechanical excitation can be applied to the distalsurface of the second object and a force for advancing the at least oneprotrusion into the region of low density can be applied to the firstobject. Such an arrangement of mechanical excitation and force foradvancing the protrusion(s) into the second object can be used togenerate a density profile in the region of low density, in which themaximal densification is generated at the distal end of the protrusionsand not at the distal surface of the second object.

The distal surface of the second object can be the distal surface of theregion of low density. For example, the second object can consist of theregion of low density at least at positions at which the first object isto be bond to the second object.

The force for advancing the at least one protrusion into the region oflow density can be or cause the mechanical pressing force needed forliquefying the thermoplastic material.

In particular, the depth of the bonding area is smaller than a thicknessof the second object that is defined as the distance between itsproximal and distal surface, wherein any compressing effects that cancause the thickness of the second object to decrease during bonding ofthe first object to the second object are considered.

However, this does not imply that the protrusions have a length smallerthan the thickness of the second object. In other words, the protrusionscan have a length along the axis along which the first object is forcedinto the second object that is larger than the thickness of the secondobject. This is because of penetration of thermoplastic material intostructures of the second object and hence in directions that aredifferent from the axis.

In embodiments in which the distal surface of the second object isformed by a layer different from the proximal surface and/or a corelayer, the depth of the bonding area can be such that the bonding areais not in contact with the layer forming the distal surface. Inparticular, the method of bonding the first object to the second objectdoes not rely on any physical property of the layer.

The above mentioned stopping surface, mark, time duration of themechanical pressing force applied prior to applying the mechanicalexcitation as well as any combination of them are examples of firstobjects and embodiments of the method adapted such that the distalsurface is unaffected by the bonding.

The use of mechanical oscillations with an amplitude not sufficient tocause liquefaction of the thermoplastic material in combination with themechanical pressing force used to force the first object into the secondobject can help to reduce at least one of the mechanical pressing forceneeded for forcing the first object into the second object, themechanical load on the distal surface, and the stress induced into thesecond object and on the distal surface of the second object.

In an embodiment, the second object provided includes a thermoplasticmaterial capable to liquefy when exposed to mechanical pressure andmechanical excitation as applied in the method. The step of applying themechanical excitation can then include an at least partial liquefactionof the thermoplastic material of the second object such that a weld isformed by the liquefied thermoplastic material of the second object andliquefied thermoplastic material of the first object afterresolidification of the thermoplastic materials.

The meltability of the second object can be such that the structure ofthe second object changes.

For example, the second object can include thermoplastic fibers, e.g.,as disclosed above. Then, the thermoplastic fibers can melt together inthe region around the protrusion(s) due to the impact of mechanicalpressing force and mechanical excitation applied. In other words: thethermoplastic fibers connect in the region.

Such a change of the structure of the second object reinforces, inparticular strengthens and stiffens, the bonding location between thefirst and second object. In other words: the quality of the bondingbetween the first and the second object can be increased by thecomposition of the second object, in particular by the composition ofthe region of low density.

At least one of the following features can be advantageous in order topromote the change in the structure of the second object:

-   -   A high concentration of thermoplastic materials, for example        thermoplastic fibers, in the region of the second object that        becomes the bonding location.    -   The melting point of the thermoplastic material of the second        object is similar to or lower than the melting point of the        thermoplastic material of the first object.

Such a weld can also be formed in the third object.

In an embodiment in which the second object includes, for example,natural or synthetic fibers that are embedded in a plastic, the plasticcan be the thermoplastic material of the second object.

For example, the second object can be produced by a method including thesteps of:

-   -   Providing fibers of a first kind and fibers of a second kind,        wherein the fibers of the first kind have a melting temperature        that is lower than the melting temperature of the fibers of the        second kind.    -   Mixing the fibers of the first and second kind, such that an        assembly of fibers of the first and second kind is generated.    -   Heating the assembly of fibers of the first and second kind to        such a temperature that the fibers of the first kind meld at        least partly and embed the non-melting fibers of the second        kind.

In an embodiment of the method in which a weld between the first and thesecond object is formed, the weld can be formed between thethermoplastic material of the first object and the fibers of the firstkind (that flowed together), between the thermoplastic material of thefirst object and the fibers of the second kind, or between thethermoplastic material of the first object and both the fibers of thefirst and second kind.

Between which components the weld is formed and where in the assembly ofthe first and second object it is formed depends on the physicalproperties (in particular melting temperature and compatibility) of thecomponents and the shape and relative arrangement of the first andsecond object.

In an embodiment, the fiber of the first kind includes or consists ofPolypropylene.

The first object can be a glass fiber reinforced plastic (e.g.,Polypropylene) connector, for example.

If the first object is a glass fiber reinforced plastic (e.g.,Polypropylene) connector and the fibers of the first kind consist of thesame plastic (e.g., Polypropylene), the location of the weld can bearranged easily by defining the location of maximum heating, e.g., byshape of the coupling-out face, the shape of the coupling-in face and/orthe use of energy directors.

The weld can be formed in addition to the interpenetration of liquefiedthermoplastic material of the first object into the structures of thesecond object.

In an embodiment, the second object is provided within a mold that isadapted to a desired shape of the second object. The step of applyingthe mechanical pressing force and the mechanical excitation can becarried out on the second object supported by the mold. This can avoid adeformation of the distal surface of the second object due to pressureapplied during the bonding of the first object to the second object.

The invention further concerns a device suitable for being bond to anitem by the method in any embodiment. Thereby, the device corresponds tothe first object and the item corresponds to the second object.

The device can include any feature disclosed in relation to the firstobject.

The device extends between a proximal end and a distal end and includesa device body that forms a proximal surface and a distal surface. Thedevice includes a plurality of protrusions that protrude from the distalsurface.

The device further includes thermoplastic material in a solid state. Inparticular, the protrusions include the thermoplastic material at outersurfaces.

The protrusions can include a core of a harder material (as describedabove) around which the thermoplastic material is arranged.

Alternatively, the protrusions, the protrusions and the device body orthe device consist of the thermoplastic material.

Each protrusion can taper towards one or more point, i.e. being a tip ormulti-tip, or towards a line, i.e., being ridge-like, wherein the linecan be straight or bent.

The protrusions can taper continuously or step-like.

The protrusions can form energy directions structures by their overallshape, for example by being tapered or by including steps and/or theycan include a structure that serve as an energy director exclusively.

In an embodiment, the device includes a stopping surface generated bythe portion of the distal surface that does not support the protrusions.

In particular, the protrusions protrude essentially normal to the distalsurface such that the stopping surface runs essentially perpendicular toan axis along which the protrusions extend, for example taper.

In particular, the stopping surface is formed by the portion of thedistal surface between the protrusions. However, one can also envisageto arrange the protrusions such that a protrusion is in direct contactto its neighboring protrusion(s). In this embodiment, the stoppingsurface is reduced to a line running between the protrusions.

In an embodiment, the device is a connector. For example, the devicefurther includes an element of a connecting device and/or the devicebody is such that a further object can be attached, for example bondedor anchored in the device body.

The element can be an element of a mechanical and/or electricalconnecting device.

In particular, the connector can be equipped to attach a further objectto the proximal end of the connector, wherein the connector is boned tothe item at its distal end.

For example, the element of the connecting device is arranged on theproximal surface such that a counter element of the connecting devicethat is arranged on the further object can engage with it.

The connector can include a proximal functional structure. This means afunctional structure arranged on or in the proximal surface of thedevice body.

The proximal functional structure may be a connecting structure defininga connecting location, especially a connecting location defined withrespect to all dimensions (x, y, z).

The functional structure (the connecting location if the functionalstructure is a connecting structure) may be off-center with respect toan insertion axis so that the orientation of the connector around itsinsertion axis (generally the proximodistal axis that may be centralwith respect to the device body and/or protrusion region) determines theposition and orientation of the connecting location. In this, thefunctional structure is, for example, different from a fastening hole(with our without a thread) coaxial with the axis, from a coaxial peg orthreaded bar protruding towards proximally, from a head, etc., or anyother conventional fastening structure of a known fastener.

The method may include bonding the connector relative to the secondobject in a well-defined x, y and z position, and in a well-definedorientation.

To this end, one or more of the following measures may be implemented:

-   -   The tool by which the mechanical pressing force and, as the case        may be, the mechanical excitation is applied includes a position        control that stops the process when the connector has reached a        well-defined z position.    -   The connector has the stopping surface, this means a distally        facing abutment face, and the process stops in a condition in        which the stopping surface rests against the proximal surface of        the second object, or against a corresponding proximally facing        structure of the second object, or a mechanical resistance        against a further forward movement of the connector towards the        second object has reached a certain value (force control), or        the proximal surface of the device body (or a portion of it) is        flush with a portion of the proximal surface of the second        object.    -   The connector has a not rotationally symmetric (about the        insertion axis) guiding structure cooperating with a        corresponding structure of the tool to define the orientation.        -   The coupling-in face of the connector can include or form            the guiding structure.        -   The coupling-out face of the tool, in particular of the            sonotrode, can include or form the corresponding structure.    -   The connector has a distal guiding structure that is not        rotationally symmetric about the insertion axis and that        cooperates with an according not rotationally symmetric        positioning hole of the second object.

More in general, the functional structure can be part of a functionalportion that further can include a distally facing abutment structure,wherein the mechanical pressing force or a mechanical pressing force isapplied until the abutment structure abuts against the proximal surfaceof the second object or a portion of the proximal surface. Such abutmentstructure may be the distal surface of a plate-like device body, or itmay be constituted by another feature of the functional portion. Theabutment portion defines a separation plane between the distalprotrusion(s) and the proximal functional portion.

In particular, the connector can include the proximal functionalstructure in combination with the protruding region including aplurality of protrusions, this means a plurality of separated bodinglocations.

In an embodiment, the device or more generally the first object caninclude a cutting structure. In particular, the protrusion(s) can beformed to include the cutting structure.

A device (first object) as used in any embodiment of the methoddescribed above includes natural oscillations. These naturaloscillations can effect adversely the device, in particular the devicebody (first object body) when the mechanical excitation used to liquefythe thermoplastic material are mechanical oscillations of a frequencythat allow excitation of a natural oscillation. In other words,destructive natural oscillations can be excited in the device.

In embodiments of the device (of the first object respectively), thedevice includes features capable to avoid or damp destructive naturaloscillations. For example, the device includes at least one of:

-   -   A damping element arranged at the distal surface of the device        body. In particular, the damping element is designed to get in        contact with the second or third object during the method.    -   A fixation element including fixation element connection means        and a connecting element including connection element connection        means. The fixation element connection means and the connection        element connection means are adapted to each other in a manner        that the connection element connection means can be rigidly        connected to the fixation element connection means at least when        the fixation element is fixed to the item.        -   A method that includes the step of providing a first object            including the fixation element and the connecting element            can include a second step of applying a mechanical pressing            force and a mechanical excitation after the step of applying            the mechanical pressing force and the mechanical excitation            used to form the positive-fit connection between the first            and second object. In this case, the positive-fit connection            is formed between the fixation element and the second            object. The second step of applying a mechanical pressing            force and a mechanical excitation yields a bond between the            fixation element and the connecting element, in particular            by use of the fixation element connection means and the            connection element connection means. The fixation element            and the connecting element can be designed so that no            destructive natural oscillations are excited in the            connecting element during the second step of applying a            mechanical pressing force and a mechanical excitation.            However, one can also envisage other means not including            thermoplastic material to bond the connecting element to the            fixation element, for example snap locks, bayonet locks,            clamp devices.    -   A plurality of protrusion regions that are separate from each        other.        -   It has been found that the frequency of natural oscillations            of the device body (the first object body) can be tuned away            from the frequency of the mechanical excitation needed and            applied to cause liquefaction of the thermoplastic material            by arranging a plurality of distinct protrusion regions on            the distal surface of the first object body. In particular,            the frequency of the natural oscillations can be tuned by            the distance between the distinct protrusion regions, the            number of distinct protrusion regions and the areas that the            distinct protrusion regions cover on the distal surface of            the first object body.        -   Further, the energy of the mechanical excitation needed to            liquefy the thermoplastic material can be reduced by            arranging a plurality of distinct protrusion regions on the            distal surface of the first object body rather than a large,            non-interrupted protrusion region. This reduces the energy            needed liquefy the thermoplastic material and can therefore            avoid that an excited natural oscillation becomes            destructive.    -   A device body being non-homogenous in its physical properties.        -   This features includes device bodies that include voids            (openings). In particular, the voids can be such that the            shape of the device body is adapted to the shape of the            coupling-out face of the sonotrode.

Natural oscillation of the kind described above, destructivedeformations, this means deformations that lead to material failure dueto stress, and the combination thereof can be generated in a thirdobject that is to be fixed to the second object by the first object.

In particular, this is the case when the third object is rigid, forexample a metal sheet, and/or if the third object does not includeopenings for the protrusion(s) of the first object or openings that arenot adapted to the protrusion(s). An opening can be non-adapted to aprotrusion by having a smaller diameter than a diameter of theprotrusion or by being not a through bore, wherein a length of theprotrusion is larger than a depth of the opening.

Uncontrolled material failure of the third object during the method caneffect adversely the reliability of an item including the third objectthat is bond to the second object by the first object as such materialfailure can be the origin of a failure of the item. For example, crackscan enlarge and propagate during use of the item.

Destructive natural oscillation and destructive deformations can beavoided by designing the first object appropriately. In particular, thefirst object can include at least one of the following features:

-   -   The first object includes an arrangement of protrusions that is        capable to damp natural oscillations of the third object and/or        that is capable to prevent the third object from deforming at        critical positions.        -   The protrusions can be of a same length, this means they can            extend equally to the distal direction.        -   In an embodiment, the first object can include a first row            of protrusions and a second row of protrusions. The rows can            follow a straight or bent line. The rows can run parallel to            each other.    -   The distal surface of the first object can include regions that        are offset from each other in the distal direction.        -   For example, the region between a first and second row can            be offset from another region on the distal surface of the            first object.    -   The first object can include a damping element arranged at the        distal surface of the first object. In particular, the damping        element can be designed to get in contact with the third object        during the method.        -   The protrusions of a row can form the damping element.            However, a single protrusion can be enough to damp natural            oscillations. The exact design of the damping element            depends on various parameters, such as the size of the first            object, the size and material of the third object, etc.

In this text the expression “thermoplastic material being capable ofbeing made flowable e.g., by mechanical vibration” or in short“liquefiable thermoplastic material” or “liquefiable material” or“thermoplastic” is used for describing a material including at least onethermoplastic component, which material becomes liquid (flowable) whenheated, in particular when heated through friction i.e., when arrangedat one of a pair of surfaces (contact faces) being in contact with eachother and vibrationally moved relative to each other, wherein thefrequency of the vibration has the properties discussed hereinbefore. Insome situations, for example if the first object itself has to carrysubstantial loads, it may be advantageous if the material has anelasticity coefficient of more than 0.5 GPa. In other embodiments, theelasticity coefficient may be below this value, as the vibrationconducting properties of the first object thermoplastic material do notplay a role in the process. Especially, since the profile body may havea relatively small extension in the proximodistal direction and sincetherefore the method is also suitable for fixing a relatively thin firstor second object to the second or first object (including thepossibility of both objects being thin), the approach of the inventionmay also work for thermoplastic materials that are poor vibrationconductors, such as thermoplastic materials with a low modulus ofelasticity and/or with elastomeric properties. This is especially thecase since the shape of the profile body may ensure that the contactwith the respective object is essentially line-shaped. This has a highenergy concentrating effect, making a local liquefaction possible evenif the thermoplastic material has strong damping properties.

Thermoplastic materials are well-known in the automotive and aviationindustry. For the purpose of the method according to the presentinvention, especially thermoplastic materials known for applications inthese industries may be used.

A thermoplastic material suitable for the method according to theinvention is solid at room temperature (or at a temperature at which themethod is carried out). It preferably includes a polymeric phase(especially C, P, S or Si chain based) that transforms from solid intoliquid or flowable above a critical temperature range, for example bymelting, and re-transforms into a solid material when again cooled belowthe critical temperature range, for example by crystallization, wherebythe viscosity of the solid phase is several orders of magnitude (atleast three orders of magnitude) higher than of the liquid phase. Thethermoplastic material will generally include a polymeric component thatis not cross-linked covalently or cross-linked in a manner that thecross-linking bonds open reversibly upon heating to or above a meltingtemperature range. The polymer material may further include a filler,e.g., fibers or particles of material which has no thermoplasticproperties or has thermoplastic properties including a meltingtemperature range which is considerably higher than the meltingtemperature range of the basic polymer.

In this text, generally a “non-liquefiable” material is a material thatdoes not liquefy at temperatures reached during the process, thusespecially at temperatures at which the thermoplastic material of thefirst object is liquefied. This does not exclude the possibility thatthe non-liquefiable material would be capable of liquefying attemperatures that are not reached during the process, generally far (forexample, by at least 80° C.) above a liquefaction temperature of thethermoplastic material or thermoplastic materials liquefied during theprocess. The liquefaction temperature is the melting temperature forcrystalline polymers. For amorphous thermoplastics the liquefactiontemperature (also called “melting temperature” in this text) is atemperature above the glass transition temperature at which the becomessufficiently flowable, sometimes referred to as the ‘flow temperature’(sometimes defined as the lowest temperature at which extrusion ispossible), for example the temperature at which the viscosity drops tobelow 10⁴ Pa*s (in embodiments, especially with polymers substantiallywithout fiber reinforcement, to below 10³ Pa*s)), of the thermoplasticmaterial.

For example, non-liquefiable material may be a metal, such as aluminiumor steel, or a hard plastic, for example a reinforced or not reinforcedthermosetting polymer or a reinforced or not reinforced thermoplasticwith a melting temperature (and/or glass transition temperature)considerably higher than the melting temperature/glass transitiontemperature of the liquefiable part, for example with a meltingtemperature and/or glass transition temperature higher by at least 50°C. or 80° C.

Specific embodiments of thermoplastic materials are: Polyetherketone(PEEK), polyesters, such as polybutylene terephthalate (PBT) orPolyethylenterephthalat (PET), Polyetherimide, a polyamide, for examplePolyamide 12, Polyamide 11, Polyamide 6, or Polyamide 66,Polymethylmethacrylate (PMMA), Polyoxymethylene, orpolycarbonateurethane, a polycarbonate or a polyester carbonate, or alsoan acrylonitrile butadiene styrene (ABS), anAcrylester-Styrol-Acrylnitril (ASA), Styrene-acrylonitrile, polyvinylchloride (PVC), polyethylene, polypropylene, and polystyrene, orcopolymers or mixtures of these.

In embodiments in which both, the first and the second object includethermoplastic material and no welding is desired, the material pairingis chosen such that the melting temperature of the second objectmaterial is substantially higher than the melting temperature of thefirst object material, for example higher by at least 50°. Suitablematerial pairings are, for example, polycarbonate or PBT for the firstobject and PEEK for the second object.

In addition to the thermoplastic polymer, the thermoplastic material mayalso include a suitable filler, for example reinforcing fibers, such asglass and/or carbon fibers. The fibers may be short fibers. Long fibersor continuous fibers may be used especially for portions of the firstand/or of the second object that are not liquefied during the process.

The fiber material (if any) may be any material known for fiberreinforcement, especially carbon, glass, Kevlar, ceramic, e.g., mullite,silicon carbide or silicon nitride, high-strength polyethylene(Dyneema), etc.

Other fillers, not having the shapes of fibers, are also possible, forexample powder particles.

Mechanical vibration or oscillation suitable for the method according tothe invention has preferably a frequency between 2 and 200 kHz (evenmore preferably ultrasonic vibration having a frequency between 10 and100 kHz, or between 20 and 40 kHz) and a vibration energy of 0.2 to 20 Wper square millimeter of active surface. The vibrating tool (sonotrode)is e.g., designed such that its contact face oscillates predominantly inthe direction of the tool axis (longitudinal vibration) and with anamplitude of between 1 and 100 μm, preferably around 30 to 60 μm. Suchpreferred vibrations are e.g., produced by ultrasonic devices as e.g.,known from ultrasonic welding.

In this text, the terms “proximal” and “distal” are used to refer todirections and locations, namely “proximal” is the side of the bond fromwhich an operator or machine applies the mechanical vibrations, whereasdistal is the opposite side. A broadening of the connector on theproximal side in this text is called “head portion”, whereas abroadening at the distal side is the “foot portion”.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, embodiments of the invention are described referring todrawings. The drawings are all schematic and not to scale. In thedrawings, the same reference numbers refer to same or analogouselements. The drawings are used to explain the invention and embodimentsthereof and are not meant to restrict the scope of the invention. Termsdesignating the orientation like “proximal”, “distal”, etc. are used inthe same way for all embodiments and drawings.

The drawings show:

FIG. 1 An assembly of a first and second object before bonding the firstobject to the second object;

FIG. 2 The first object and the second object during the bondingprocess;

FIG. 3 a A sectional view of an exemplary bonding location;

FIGS. 3 b-3 d A sectional view of another exemplary bonding location atthree stages of the bonding process;

FIGS. 4 and 5 Exemplary embodiments of the first object;

FIGS. 6 and 7 An exemplary embodiment of a first object including anelement of a connection device;

FIGS. 8 and 9 An exemplary embodiment of a first object forming theelement of the connection device;

FIGS. 10-13 An exemplary embodiment of the method of bonding the firstobject to a second object including an increasing density along an axisof forcing the first object into the second object;

FIGS. 14 and 15 A sectional view of a third object attached to thesecond object by use of the first object and an embodiment of themethod;

FIG. 16 A further embodiment of the first object;

FIGS. 17 a-17 e Further embodiments of the first object including astructure for promoting local compression of the second object;

FIG. 18 A sectional view of an object attached to the second object byuse of the first object, a further object and an embodiment of themethod;

FIGS. 19 a and 19 b A sectional view of a third object before and afterits attachment to the second object by use of the first object;

FIGS. 20 a and 20 b A sectional view of a first object before and afterits attachment to a second object including a rigid proximal top layer;

FIGS. 21 a and 21 b A sectional view of an exemplary embodiment of afirst object including protrusions of different length before and afterits attachment to a second object;

FIGS. 22 and 23 Sectional views of further exemplary embodiments of afirst object including protrusions of different length after itsattachment to a second object;

FIG. 24 An exemplary embodiment of the method including a support forthe second object;

FIGS. 25 a and 25 b An exemplary embodiment of a second object designedfor protecting edges of the first object;

FIGS. 26 a-26 e Sectional views of the attachment of a third object tothe second object by use of the first object at different stages of thebonding procedure;

FIGS. 27 a-27 d Sectional views of the attachment of another thirdobject to the second object by use of the first object at differentstages of the bonding procedure;

FIG. 28 An exemplary embodiment of a first object including a pluralityof protrusions, wherein a volume of the plurality of protrusions islimited;

FIGS. 29 a and 29 b A sectional view of a first object being bonded to afurther type of the second object before and after bonding;

FIGS. 30 a and 30 b A sectional view of yet another type of a secondobject and a first object being bonded to this type of second objectbefore and after bonding;

FIG. 31 A sectional view of a further third object being bonded to thesecond object by the use of a first object;

FIGS. 32 a and 32 b Sectional views of a first object being bonded to asecond object by a method including the step of providing an adhesive;

FIGS. 33 a and 33 b An exemplary embodiment of a first object being aconnector;

FIGS. 34-39 Various exemplary embodiments of the protrusion region ofthe first object and the device, respectively;

FIGS. 40-43 Various exemplary embodiment of the first object and thedevice, respectively;

FIGS. 44-46 Three exemplary embodiments of the first object equipped forpreventing the generation of destructive natural oscillations;

FIGS. 47-49 Exemplary embodiments of first objects including a fixationelement and a connecting element;

FIGS. 50 and 51 An alternative fixation of the third object to thesecond object by the first object;

FIGS. 52 and 53 Sectional views of the attachment of a third object tothe second object by the use of a first object;

FIGS. 54 a and 54 b Sectional views of the attachment of a metal sheetwithout pre-drilled openings to the second object by use of the firstobject;

FIG. 55 An exemplary embodiment of a first object that can be used in amethod according to FIGS. 54 a and 54 b;

FIG. 56 A basic arrangement of the first and second object beforebonding the first object to the second object by applying a sonotrode tothe second object;

FIGS. 57 a and 57 b Exemplary application of the method according toFIG. 56 before and after bonding;

FIG. 58 An embodiment of the method in which the sonotrode is applied tothe second object and a force for advancing the protrusion into theregion of low density is applied to the first object; and

FIG. 59 Two representative stress-strain-curves for a panel formed by anincoherent material.

DETAILED DESCRIPTION OF THE INVENTION

A method according to the invention includes providing a first object 1,providing a second object 2 and arranging the first object relative tothe second object such that the first object 1 is in physical contactwith a proximal surface 4 of the second object 2 and such that anassembly of the first and second object is formed. An exemplaryembodiment of such an assembly is shown in FIG. 1 .

In the embodiment shown, both the first object 1 and the second object 2expand over an extended area. The first object 1 can be of the same sizeas the second object. However, it is also possible that the first object1 covers the proximal surface 4 of the second object 2 partly and/orlocally, only.

The second object 2 and/or the first object 1 can be non-plane. Inparticular in configurations in which the second object 2 expands over alarger area than the first object 1, the second object 2 can benon-plane, for example by having a shape adapted to a shape of a surfacethat has to be covered by the second object 2, whereas the first object1 is plane. The plane first object 1 can then be bonded to a planeproximal surface region of the second object 2 or the first object 1 canbe deformed during the bonding process such that its shape becomesadapted to the shape of the second object 2.

In the embodiment shown, the first object 1 expands between a proximalend 5 and a distal end 6 and consists of thermoplastic material.

The first object 1 includes tapered protrusions 9 in the shape of ridgesat its distal end 6, in the embodiment shown in FIG. 1 .

The ridges protrude from a body 7 of the first object 1 (also calledfirst object body or device body), the body 7 forming the proximal end 5of the first object 1.

The body 7 and/or elements 15 of a connecting device attached orattachable to the body 7 can be equipped for connecting a further objectto the first object 1.

The second object 2 includes an increasing density in a direction normalto the proximal surface 4 and it includes structures 10, for examplepores, into which liquefied material can penetrate.

The increasing density can be due to a change in the composition of thesecond object 2 along the direction and/or due to a decrease in thestructures, for example.

Due to such changes, the second object 2 includes a region 22 of adensity that is lower than the density of a region 23 that is arrangeddistally of the region 22 of low density.

The region 22 of a density that is lower than the density of a region 23arranged distally of it is also called the proximal region 22, whereasthe region 23 arranged distally of the proximal region 22 is also calledthe further region 23.

In the embodiment shown in FIG. 1 , the second object 2 includes aplurality of fibers that are at least partly embedded in a plastic(enlarged part of FIG. 1 ). The portions of the fibers that are notembedded in the plastic form a soft surface layer. The soft surfacelayer has a density that is lower than the density of the second object2 in regions where the fibers are embedded in the plastic.

Hence, both the composition and the density of structures 10 change inthe direction normal to the proximal surface 4. The soft surface layercorresponds to the region 22 of low density and the regions with thefibers embedded in the plastic corresponds to region 23 of high density.

The density profile of second object 2 of FIG. 1 is shown next to theenlarged part of the second object 2. The second object 2 can includefurther density regions, for example a second region of low densityforming a proximal surface of the second object 2 or a transition regionthat extends between a region of low and high density.

As pointed out above, the region of high density can include a pluralityof structures, voids, openings, etc. Further, it can be compressible,for example compressible to a critical density and/or in a manner thatthe region of high density provides a critical compressive strength. Theterm “critical” relates to a density and/or compressive strength neededfor the liquefaction of the thermoplastic material in the method.

FIG. 2 shows the assembly of the first and second object during the stepof applying a mechanical pressing force (indicated by an arrow in FIG. 2) and mechanical oscillations (indicated by a doubled-headed arrow)along an axis 8 that is essentially perpendicular to the proximalsurface 4 of the second object 2.

The mechanical pressing force as well as the mechanical oscillations areapplied by a sonotrode 20 including a coupling-out face 21 that is inphysical contact with a proximal surface 4 of the first object 1.

In the embodiment shown, the coupling-out face 21 is designed to exposea portion of the first object 1 to mechanical oscillations and/or themechanical pressing force, only. Hence, well-defined, local bondinglocations 13 are generated during the bonding process. Four bondinglocations 13 are shown in FIG. 2 . However, the number of bondinglocations 13 depends on the shape and size of the first object 1, theshape and material of the second object 2, and the demands on the bond(e.g., its strength), for example.

An advantage of the bonding method shown is that the number andarrangement of bonding locations 13 can be adapted easily and evenduring the bonding by applying the sonotrode 20 to positions on theproximal surface of the first object 1.

In the embodiment shown, the mechanical pressing force is directed alongthe axis 8 of the mechanical oscillations, too. However, the mechanicalpressing force sets in prior to the mechanical oscillations. This hasthe effect of the protrusions 9 penetrate through the region 22 of lowdensity before being liquefied, at least. By doing so, the bonding ofthe first and second object is not restricted to the proximal surface 4only, but relies on structures 10 within the second object 2. In otherwords: Deep anchoring in contrast to surface anchoring as established byadhesives for example is generated.

The density profile of the second object 2 can be such that there is noneed to start applying the mechanical pressing force prior to themechanical oscillations. In this case, liquefaction of the thermoplasticmaterial 3 sets in as soon as the density of the second object hasreached a value that allows compression of the thermoplastic material 3to such an extent that liquefaction sets in.

The second object is shown in a schematic way in FIG. 2 , only. Thesecond object shown in FIG. 2 can correspond to the second object shownin FIG. 2, 3 or 10-13 , in particular.

FIG. 3 a shows a sectional view along the AA-axis shown in FIG. 2 andfor a second object 2 as shown in FIG. 1 .

The combined effect of mechanical pressure and mechanical oscillationhas caused the portions of the thermoplastic material 3 of theprotrusion 9 in contact with the region 23 of high density to liquefyand to penetrate into the structures 10 of the second object 2. Thisresults in a positive-fit connection, in particular in a positive-fitconnection with respect to the axis 8 of the oscillation (i.e. apositive-fit preventing a relative movement of the first and secondobjects normal to the proximal surface 4) between first and secondobject after resolidification of the liquefied thermoplastic material 3.

FIGS. 3 b-3 d show sectional views of the establishment of a bondingbetween the first object 1 and a second object 2 with a constant densityprofile in the direction perpendicular to the proximal surface 4 of thesecond object 2.

FIG. 3 b shows the situation before pushing the protrusions 9 of thefirst object 1 into the second object 2.

FIG. 3 c shows the situation during the step of pushing the protrusions9 and the body 7, if the density of the second object is such that thebody can be pushed into the second object without destroying the firstor second object and/or their properties, in the second object 2.

The penetration of the protrusions 9 and, as the case may be, the body 7compresses the second object 2 locally around the distal end of theprotrusions 9, at least. This leads to the density profile needed toliquefy the thermoplastic material 3 of the protrusions 9 by applyingthe mechanical pressing force and the mechanical excitation.

FIG. 3 d shows the situation after the step of stopping the mechanicalexcitation. Liquefied thermoplastic material 3 has penetrated into thestructures 10 of the second object 2.

The liquefied thermoplastic material 3 can penetrate regions of thesecond object 2 that are not compressed or slightly compressed only. Inthis case, the bonding of the first to the second object goes evendeeper into the second object 2 than given by a protruding portion 91that guarantees a deep-effective anchoring.

FIG. 4 shows an embodiment of the first object 1 similar to the oneshown in FIGS. 1 and 2 as it is provided in the method for bonding thefirst object 1 to the second object 2.

One can envisage protrusions 9 other than the ones shown in FIG. 4 .FIG. 5 shows an exemplary embodiment of a first object 1, wherein theprotrusions 9 are given by a plurality of tips.

The protrusions 9 protrude from a distal surface 28 of the body 7 of thefirst object 1. They are arranged in a protrusion region 90 that islocated distally of the distal surface 28 of the body 7 of the firstobject 1.

The first object 1 further includes a proximal surface 29 of the body 7of the first object 1 (hidden in FIGS. 4 and 5 , see FIGS. 6, 8 and 9 ),the proximal surface forms the proximal end 5 of the first object 1during and after the method.

The method shown in FIGS. 1-3 can be used for bonding an element 15 of aconnecting device to the second object 2. This can be done by a firstobject 1 including such an element 15.

The first object 1 can include one or more elements 15 of a connectingdevice. For example, a plurality of elements 15 can be arranged on theproximal surface of the first object 1 according to FIG. 4 or 5 .

FIG. 6 shows an exemplary embodiment of the first object 1 including anelement 15 of a connection device. FIG. 7 shows a sectional view of thefirst object 1 with applied sonotrode 20.

In the embodiment shown, the element 15 of the connection device is arod including an inner thread.

The first object 1 includes a coupling-in face 11 that is arranged onthe proximal surface of the first object 1 around the protruding element15, in the embodiment shown.

The distal end of the sonotrode 20, i.e., the end of the sonotrode 20including the coupling-out face 21, is adapted to the first object 1 byincluding an opening into which the rod can be inserted such that it isnot loaded during the bonding process.

In the embodiment of FIG. 6 , the protrusions 9 are ridge-like, again.However, the first object 1 can include protrusions that are differentlyshaped, such as tips.

The first object 1 can include one, two, three or four tips, forexample. A small number of protrusions 9 can be sufficient inembodiments in which the first object 1 is small and/or defines onebonding location 13 by itself, as shown in FIG. 7 .

Again, the protrusions 9 are arranged in a protrusion region 90 distallyof the distal surface 28 of the body 7 of the first object 1.

The area of the coupling-out face 21 can be equal to or larger than thearea of the proximal surface, in particular if the first object 1defines one bonding location 13 by itself.

FIGS. 8 and 9 shows a schematic view and a sectional view of a firstobject 1 that is in fact a connector 16. In other words, the firstobject 1 includes an element of a latching mechanism mounted on athermoplastic device that is capable of being bonded to the secondobject 2 by any embodiment of the bonding method.

FIG. 9 shows a sectional view of the first object 1. In the exemplaryembodiment shown, the protrusions 9 are separated from each other bygaps 27 that extend down to the proximal surface 29 of the body 7 of thefirst object 1.

In the embodiment shown, the protrusions 9 are arranged and designedsuch that flat regions of the proximal surface 29 extend between them.The flat surfaces can act as stopping surfaces.

FIGS. 10-12 shows an embodiment of the method in which the first object1, e.g., a first object 1 according to FIGS. 4-9 , penetrates into theregion of high density before the liquefaction of the thermoplasticmaterial 3 sets in.

In FIGS. 10-13 , the second object includes a proximal surface layer 17,a distal surface layer 18 and a core layer 19, wherein the density ofthe distal and proximal surface layer is lower than a density of thecore layer 17. However, the method described in the following is alsosuitable for a second object 2 with a density profile that is generateddifferently, for example for the second object 2 according to FIG. 1 .

For example, the proximal and distal surface layers include oressentially consist of a damping material, whereas the core layer 17consists of the damping material embedded in another material or it iscomposed by materials other than the damping material. The othermaterials are denser than the damping material and they can show ahigher mechanical stability than the damping material.

FIG. 10 shows the situation after the step of applying to the firstobject 1 a first mechanical pressure force (indicted by the small arrowon top of FIG. 10 ) that is smaller than a second mechanical pressureforce applied to the first object 1 in a subsequent step of the method.No mechanical oscillations have been applied, so far.

The protrusions 9 of the first object 1 have penetrated through theproximal surface layer 17 but not into the core layer 19.

FIG. 11 shows the situation during the step of applying the secondmechanical pressure force (indicted by the large arrow on top of FIG. 11). No mechanical oscillations have been applied, so far.

The protrusions 9 have penetrated into the core layer 19 and are capableto penetrate into the core layer 19, further. This means, the movementof the first object 1 relative to the second object 2 along thepenetration axis is not prevented by any element of the first or secondobject.

In particular, an optionally present stopping surface does not yetgenerate a counter force to the pressure force applied such that afurther penetration of the first object 1 into the second object 2 isprevented.

If the stage shown in FIG. 11 is established, the mechanicaloscillations (indicated by the doubled-headed arrow) are applied.

FIG. 12 shows the situation after the bonding process. Thermoplasticmaterial 3 has penetrated into structures 10 of the core layer 19 andforms a positive-fit connection between the first and second object, inparticular a positive-fit connection normal to the penetration directionof the first object 1.

However, the protrusion 9 has not disappeared completely, for example bybeing “smeared out” during the method. Rather the protruding portion 91resists at the position at which the protrusion 9 was before applyingthe mechanical oscillations. This leads to a deep effective anchoring,for example.

The stopping surface 12 generated a counterforce to the secondmechanical pressure force in a final phase of the bonding process,wherein the counterforce was such that the movement of the first object1 towards the distal surface layer 18 was limited. Hence, a maximumpenetration depth of the first object 1 into the second object 2 isdefined by the stopping surface 12 and the length of the protrusions 9normal to the stopping surface.

In the embodiment shown, the stopping surface 12 is a surface of thefirst object 1 that expands normal to the penetration direction of thefirst object 1, i.e. normal to the axis 8 of the mechanicaloscillations.

In the embodiment shown, the length of the protrusions 9 is such that adistal surface 14 of the second object 2 is neither in contact noraffected by the thermoplastic material 3. Further, the density of thecore layer 19 (the region 23 of high density) at any bonding location 13at least is such that liquefaction of the thermoplastic material ispossible without need for a further material or surface being involved.

The core layer shown 19 includes a material or consists of a compositethat generates the mechanical stability of the second object 2. Thesecond object 2 can be bendable, in particular elastically bendable.Nevertheless, the material or composite of the core layer 19 is suchthat the thermoplastic material 3 can liquefy at an interface betweenthe thermoplastic material 3 and the material or composite of the corelayer 19 under the effect of mechanical oscillations and the mechanicalpressure force. In particular, the material or composite includes therigidity needed for the liquefaction.

In particular, the physical properties of the distal layer 18 areneither needed nor involved in the liquefaction of the thermoplasticmaterial 3.

FIG. 13 shows the bonding establish by a method according to FIGS. 10-12but without applying the second mechanical pressure or with simultaneousapplication of the second mechanical pressure force and the mechanicaloscillations.

The penetration depths of the thermoplastic material 3 is limited to theproximal surface region 17 and adjacent regions of the core layer 19.

FIGS. 14 and 15 show sectional views through an assembly of a firstobject, second and third object, wherein the third object 30 is attachedto the second object 2 by the first object 1 and wherein the firstobject 1 is bonded to the second object 2 by an embodiment of themethod.

The third object 30 includes a third object proximal surface 31 and athird object distal surface 32. The third object 30 is arranged relativeto the second object 2 such that its distal surface 32 is in physicalcontact to the proximal surface 4 of the second object 2.

In the embodiment shown in FIG. 14 , the third object 30 can have anydensity profile from the third object proximal surface 31 to the thirdobject distal surface 32 that can be penetrated by the protrusion(s) 9of the first object 1.

In particular, the third object 30 can have any density profiledescribed in respect of the second object 2.

Hence, it is possible that the first object 1 is bonded to the thirdobject 30 by the use of the corresponding steps of the method andcorresponding structures 35 of the third object 30.

In the embodiment shown in FIG. 15 , the third object 30 includes aregion 36 of low density at its proximal surface 31, too. Further, thefirst object 1 includes a protrusion 33 of a first kind and a protrusion34 of a second kind.

The protrusion 33 of the first kind has a length and a diameter suchthat the distal end of the protrusion 33 of the first kind penetratesthe region 22 of low density of the second object 2 at least partly andsuch that the distal end of the protrusion 33 of the first kindpenetrates into structures 10 of the second object 2 during the bondingprocess.

The protrusion 34 of the second kind has a length and a diameter suchthat the distal end of the protrusion 34 of the second kind penetratesthe region 36 of low density of the third object 30 at least partly andsuch that the distal end of the protrusion 34 of the first kindpenetrates into structures 35 of the third object 30 during the bondingprocess.

In particular, the diameter of the protrusion 33 of the first kind islarger than the diameter of the protrusion 34 of the second kind.

FIGS. 16 and 17 a-17 e show exemplary embodiments of the first object 1.

The embodiment shown in FIG. 16 corresponds to the embodiment providedin a method leading to the assembly of the first, second and thirdobject as shown in FIG. 15 .

FIGS. 21-23 show other configurations in which embodiments of the firstobject 1 according to FIG. 16 can be used.

There is no need for cross-sectional areas of the protrusion 33 of thefirst kind and the protrusion 34 of the second kind that are identicaland/or that are circular.

However, in many embodiments of the first object 1 shown in FIG. 16 ,the cross-sectional area of the protrusion 33 of the first kind islarger than the cross-sectional area of the protrusion 34 of the secondkind.

FIG. 16 indicates a thickness 26 of the protrusions 9 and theirextension 25 in distal direction. The extension is equal to the distanceof the most distal point of the protrusion to the distal surface 28 ofthe body 7 of the first object 1. The embodiments of the first object 1shown in FIGS. 17 a-e do not only increase locally the density of thesecond object 2 by the protrusion displacing material of the secondobject 2 (for example as shown in FIGS. 3 b-3 d ) but also by includingstructures 24 that are designed and arranged specifically to promotelocal compression of the second object 2, in particular of the region 22of low density.

Further, the structures 24 shown are designed and arranged to pull downfibrous material of the second object 2 and/or to felt such materialfurther and/or to embed the protrusions 9 including such structures 24better in the material of the second object 2, for example fordistributing any load over a larger area.

The embodiments of the first object 1 shown in FIGS. 17 a, 17 b and 17 einclude so-called barbs 24, i.e., structures that have a shape and arearranged at the protrusion 9 such that they are capable to increase thedensity of the second object 2 faced by the protrusion 9 in function ofthe penetration depth of the protrusion 9.

The barbs can be arranged at a distal end of the protrusion 9, as shownin FIG. 17 a . This leads to a local compression of the second object 2that favours the liquefaction of the thermoplastic material 3 arrangedaround the distal end of the protrusion.

Alternatively or in addition, the barbs 24 can be arranged at thelateral side of the protrusion 9. As examples, FIG. 17 b show drag downbarbs that are small compared to the size of the protrusion 9 and FIG.17 e show catching barbs that have a size such that they contribute tothe overall shape of the protrusion.

There is no need for a homogenous distribution of the barbs 24 at thelateral side. Rather, the barbs 24 can be arranged such that theliquefaction of the thermoplastic material 3 sets in at certainpositions on the protrusion 9 and/or that the penetration of the secondobject 2 by liquefied thermoplastic material is restricted along aspecific direction.

In FIGS. 17 c and 17 d , the structure 24 designed and arranged topromote local compression of the second object 2 is given by the shapeof the distal end of the protrusion, in particular by having multipletips that cause catching of fibers, for example.

In particular, barbs are suitable for use in fibrous second objects 2where they can collect fibers during penetration and hence increase thedensity of fibers around the protrusion 9.

The barbs can be made of the thermoplastic material 3 or a hardermaterial.

Barbs made of the thermoplastic material 3 can increase the embedding ofthe protrusion 9 and the protruding portion 91 respectively, further.

Barbs can also be arranged at the protrusion 33 of the first kind and/orat the protrusion 34 of the second kind.

The first object 1 shown in FIGS. 14-17 can further include at least oneelement 15 of a connecting device.

The first object 1 shown in FIGS. 14-17 can be a connector as describedabove.

FIG. 18 shows a sectional view of the result of an embodiment of themethod in which an object 100 different to the first and second objectis attached to the second object by connecting a further object 40 tothe first object 1.

In the embodiment shown, the first object 1 is a reinforcement element.

The further object 40 is a fixing element, such as a nail, that has adistal end 41 in the shape of a tip. The further object 40 includingfurther an attachment location 42 that is arranged to penetrate theobject 100 to be attached to the second object 2 and to penetrate intothe body 7 of the first object 7.

The first object 1 is bonded to the second object 2 by the method in anyone of the embodiments described previously. In particular, the firstobject 1 is bonded to the second object 2 by a method that results inthe protruding portion 91 being present in the second object after thestep of stopping the mechanical excitation and letting the thermoplasticmaterial solidify.

FIG. 19 a shows a sectional view of a third object 30 before itsattachment to the second object 2 by bonding the first object 1 to thesecond object 2. In the embodiment depicted, the third object includesthermoplastic material in the regions at which the third object 30 ispierced by the protrusions 9, at least. For example, the third object 30shown in FIG. 19 can be a thermoplastic foil.

FIG. 19 b shows a sectional view of the third object 30 attached to thesecond object 2. A weld 203 is formed between the first object 1 and thethird object 30 during the method of bonding the first object 1 to thesecond object 2. This is a result of the third object 3 includingthermoplastic material in the regions at which it is pierced by theprotrusion.

The thermoplastic material of the third object 30 as well as thethermoplastic material 3 of the first object 1 arranged at the proximalend of the protrusions 9 and/or the neighbouring thermoplastic materialof the distal surface 28 of the body 7 are such that they liquefy underthe mechanical pressing force and mechanical excitation applied.However, one can envisage that the condition for liquefaction of thethermoplastic material(s) is only met after compression of the secondobject 2 by pushing the body 7 into the second object 2.

FIG. 19 b shows a mechanism that is able to increase the quality of thebond between the first and second object further. Although shown incombination with establishing a weld 203 between the first and the thirdobject, the mechanism can be used in any embodiment of themethod—independent of the presence of a third object 30.

An embodiment including the mechanism has a second object 2 thatincludes thermoplastic material in the region(s) at which a bond betweenthe first and the second object is established. The thermoplasticmaterial is capable to liquefy or at least soften under the impact ofthe mechanical pressure and mechanical excitation applied during themethod of bonding the first object 1 to the second object 2. In avariant of the embodiment, the thermoplastic material can only beliquefied/soften after its compression by pushing the protrusions 9and/or the body 7 into the second object 2.

Due to the liquefaction or soften, the second object 2 includes a region202 with changed structural properties after the step of letting the (inthis case “all”) thermoplastic material resolidify. A higher densityand/or material of the second object 2 that is better interlinked areexamples of the changed structural properties.

FIGS. 20 a and 20 b show the bonding of a first object 1 to a secondobject 2 including a proximal top layer 200 that is not part of theregion 22 of low density.

For example, the proximal top layer 200 is the rigid cover layer of ahollow core board (HCB).

FIG. 20 a shows the situation after positioning the first object 1relative to the second object 2. The protrusions 9 of the first object 2are designed to penetrate the proximal top layer 200 without deformingsignificantly. Further, they can include a distal tip or edge.

FIG. 20 b depicts the situation after bonding the first object 1 to thesecond object 2. Shown is the case in which the unaffected layerarranged distally of the proximal top layer 200 is not dense enough tolead to a liquefaction of the thermoplastic material 3 within a timeframe that is practical in professional use. Again, it is theestablishment of a compressed region 201 that makes the bonding of thefirst object 1 to the second object 2 possible.

FIGS. 21-23 show embodiments of the method including protrusions thatare adapted in length, for example adapted to a thickness of the secondobject 2, to a layered structure of the second object 2, to themechanical properties of the body 7, to the shape of the body, and/orfabrication steps following the bonding of the first object 1 to thesecond object 2.

FIGS. 21 a and 21 b show an embodiment in which the first object 1includes a protrusion 33 of a first kind and a protrusion 34 of a secondkind, wherein the protrusion 33 of the first kind is longer than theprotrusion 34 of the second kind.

The protrusion(s) 33 of the fist kind has a length that is longer thanthe thickness of the second object 2 in direction of penetration of theprotrusion 33 of the first kind into and through the second object 2.

In this case, the method includes the further step of providing an anvil60 including a deformation recess 61. The deformation recess 61 ispositioned such that the distal end of the protrusion 9 engages with thedeformation recess 61 after penetrating the second object 2. The distalend of the protrusion 9 can then be deformed in a distal head 62 byapplying mechanical pressure and mechanical excitation to the firstobject 1 or to the anvil 60.

The protrusion(s) 34 of the second kind has a length that allows forbonding the first object 1 to the second object 2 within the secondobject 2 and according to any embodiment of the method, e.g., by themethod including establishing a compressed region 201.

An arrangement of the protrusions in which the protrusions 33 of thefirst kind are arranged close to ending, this means lateral, edge 210 ofthe body 7 and the protrusions 34 of the second kind are arrangedradially inside the protrusions 33 of the first kind can be advantageousin configurations in which for example:

-   -   The body 7 of the first object 1 is not stiff enough to remain        in position over a larger area and/or over time;    -   The second object 2 is deformed after bonding the second object        2 to it in preliminary but enduring manner.

FIG. 22 shows a further arrangement of protrusions 9 of different lengthafter bonding the first object 1 to the second object 2. In theembodiment shown, the length of the remaining protruding portions 91correlate with the length of protrusions.

The embodiment shown in FIG. 22 is an example of a first object 1including protrusions that are optimized in terms of material costs andforces acting on the bond between the first and second object in aspecific application. The embodiment shown is particularly suitable forapplications in which the bonded first and second item are bent, thismeans applications that cause bending forces.

FIG. 23 shows an embodiment in which the second object 2 includes alayered structure. Again, the first object 1 includes a protrusion 33 ofa first kind and a protrusion 34 of a second kind. The length of theprotrusions is adapted such that the bond is formed either in a firstregion 204 of low density or in a second region 205 of low density thatis arranged more distally than the first 204 region of low density.

FIG. 23 shows a simple arrangement of the layers forming the secondobject 2. However, the length and arrangement of protrusions 33 of thefirst kind, protrusions 34 of the second kind and—as the case may be—ofprotrusions of further kinds can be adapted to more complex arrangementof layers. In particular, the layers do not need to run parallel to eachother, to be constant in thickness and/or to expand over the wholeexpansion of the second object 2. For example, layers, such as layers oflow density, can be arranged locally, this means only at positions atwhich the bonding of the first object 1 to the second object 2 has tooccur.

Further, there is no need that the second object 2 includes a rigidproximal top layer 200 or rigid layers 206 between regions of lowdensity.

In principle, there is no need for any rigid layer 206 or any region ofa density that gives the second object 2 load bearing capacity. In thiscase, the method can include the step of providing a support 63 duringthe method of bonding the first object 1 to the second object 2, atleast. This configuration is shown in FIG. 24 .

FIG. 24 shows the situation immediately after the liquefaction of thethermoplastic material 3 has set in. If the second object 2 includes noregion of high density at all, a compressed region 201 needs to beestablished before liquefaction of the thermoplastic material 3 sets in.

The anvil 60 is an example of such a support 63. However, the support 63can also be given by an item to which the second object 2 is attached.

FIG. 25 a shows an application of a method in which the mechanicalpressing force and the mechanical excitation are applied locally to thefirst object 1 and in which the step of applying the mechanical pressingforce and the mechanical excitation is repeated several times atdifferent positions on the first and second object 1. Hence, there areseveral bonding locations 13 that are not arranged on a single plane andthat cannot be addressed in a single step of applying the mechanicalpressing force and the mechanical excitation.

In the application shown, the first object 1 is a protection for an edgeor corner of the second object 2.

FIG. 25 b shows a sectional view of the first object 1 according to FIG.25 a attached to the second object 2. A first bonding location 13 isarranged at a first side of the second object 2 and a second bondinglocation 13 is arranged at a second side of the second object 2, whichis non parallel to the first side.

In the embodiment shown, the first object 1 is pushed into the secondobject 2 in a manner that the distal surfaces 28 of the body 7 are atthe same level as the corresponding surfaces of the second object 2.This arrangement of first and second object is not specific for theapplication shown in FIGS. 25 a and 25 b but can be realized in anyembodiment of the method including a second object 2 with a proximalsurface 4 that allows for pushing in the first object body 7.

In many embodiments, the corresponding surfaces of the second object 2are the proximal surfaces 4.

An effect of pushing the body 7 into the second object 2 such that thedistal surface(s) 28 of the body 7 is/are at the same level as thecorresponding surface(s) of the second object 2 is a global compressionof the second object 2 in the region in which the body 7 is pushed intothe second object 2, at least. The resulting compressed region 201, inparticular in combination with the local compression caused by theprotrusions 9, can be a requirement for efficient liquefaction of thethermoplastic material 3, as described above in detail.

FIGS. 26 and 27 show embodiments of a method including the further stepsof providing a third object 30 and attaching the third object 30 to thesecond object 2 by bonding the first object 1 to the second object 2according to any embodiment of the method of bonding the first object 1to the second object 2.

In the embodiment shown in FIGS. 26 and 27 , the third object 30includes a through bore 230 defining an opening 231 in a distal side ofthe third object 30.

The embodiments of the third object 30 shown in FIGS. 26 and 27 includethe optional feature of a region 232 around the through bore 230 that isbent in distal direction. Consequently, the distal opening 231 in totalor at least a part of it is displaced in distal direction with respectto portions of the third object 30 that are not arranged in closeproximity of the through bore 230.

The method shown in FIGS. 26 and 27 includes the step of bringing thedistal surface 32 of the third object 30 in contact with the proximalsurface 4 of the second object 2 and pushing the bent region 232 intothe second object 2. By doing so, the bent region 232 establishes thecompressed region 201 in a region of the second object 2 that is locatedin proximity of the bent region. Optionally, the third object 30 can bepressed further towards the second object 2 such that a globalcompressed region 201 as indicated in FIG. 26 b results.

In particular, the bent region has a mechanical stability such that itcan take the load generated during the step of pushing the bent region232 into the second object 2.

In embodiments of the method, in which a bent region 232 is pushed intothe second object 2, the method can include the further step ofproviding a pushing- and holding down device. In other words: the thirdobject 30 and/or the bent region 232 is not pushed into the secondobject 2 by a pressing force applied to the first object, but by apressing force applied to the third object 30 by the use of the pushing-and holding down device.

The compressed region 201 located in proximity of the bent region 232 isfurther compressed in the subsequent step of pushing the protrusion 9through the distal opening 231 into the second object 2. This kind ofestablishing a compressed region 201 or increase the density of acompressed region 201 has been described in detail, already. However, itis important to note, that the establishment or increase is not or notonly the result of liquefied material penetrating into the second object2 but of a solid portion of the protrusion 9 penetrating into the secondobject 2 before its liquefaction. The portion of the protrusion 9 istransformed into the protruding portion 91 during the step of liquefyingthe thermoplastic material 3.

Hence, it is the compression resulting from pushing the protrusion 9into the second object in combination with the compression resultingfrom pushing the bent region 232 into the second object 2 thatestablishes the density profile needed to liquefy the thermoplasticmaterial 3 of the protrusion 9 during the step of applying themechanical pressing force and the mechanical excitation and to bondfirst object 1 to the second object 2.

However, one can envisage to provide a third object 30 without bentregion 232 and to design the protrusion in a manner that the compressedregion 201 established by pushing the protrusion 9 into the secondobject 2 is sufficient to establish the density profile needed to causeliquefaction of the thermoplastic material 3 during the step of applyingthe mechanical pressing force and the mechanical excitation.

In FIGS. 26 a to 26 d , the third object 30 is a metal sheet, forexample an aluminum sheet, including the optional feature of the region232 around the through bore 230 that is bent in distal direction.Further, the bent region 232 is designed such that it can be deformedelastically. In particular, the rim 233 forming the distal opening 231includes notches 234 extending in proximal direction, this means towardsthe portions of the third object 30 that are not part of the bent region232. An embodiment of such a resulting bent region 232 in shown in FIG.26 e.

In embodiments including an elastically deformable bent region 232, adiameter of the protrusion 9 can be larger than a diameter of the bentregion 232. Hence, an elastic deformation in the sense of a widening ofthe bent region 232 and the rim 233 is established. This is indicated bytwo black arrows in FIG. 26 b.

The following two effects are caused after pushing at least a portion ofthe protrusion 9 through the through bore 230 (FIG. 26 c ): First, theprotrusion 9 penetrating the second object 2 effects a further localcompression of the compressed region 201 resulting from pushing the bentregion 232 into the second object 2. The protrusion 9 penetrating thesecond object 2 can cause an extension of the compressed region 201, inparticular an extension in distal direction. Second, the elasticallydeformed bent region 232 causes a compressing force 239 on a portion ofthe protrusion 9. This compressing force is indicated in FIG. 26 b bytwo black arrows.

The compressing force 239 leads to a melting zone 236 on the protrusion9 during the step of applying the mechanical pressing force and themechanical excitation at the area where the compressing force 239applies. In other words: thermoplastic material 3 of the protrusion 9liquefies due to the compressing force 239 and the mechanical pressingforce and the mechanical excitation applied during the correspondingstep. This causes an embedding of the bent region 232 in the protrusion9 (more exactly in the protruding portion 91) in addition to thepositive-fit connection established by the thermoplastic material thathas penetrated the material of the second object 2.

This means, that the method according to FIGS. 26 a-26 e includes thefurther step of embedding the bent region 232 at least partly in theprotruding portion 91.

FIG. 26 d shows a sectional view of an exemplary embodiment of anattachment based on an embodiment of the method including the furtherstep of embedding the bent region 232 at least partly in the protrudingportion 91.

FIGS. 27 a to 27 c shows another embodiment of the method including thestep of providing a third object with a bent region 232.

In the embodiment shown, the bent region 232 is designed in a mannerthat the distal opening 231 is a radial opening with respect to aninsertion axis 235 along which the first object 1 is moved relative tothe second object 2 during the method of bonding the first object 1 tothe second object 2.

Again, the compressed region 201 is established by pushing the bentregion 232 into the second object 2.

In contrast to the embodiment of FIG. 26 , the bent region 232 is notdesigned to generate a compressing force 239 to the protrusion 9.However, the bent region 232 and the protrusion 9 are designed such thatthe protrusion 9 deforms towards the distal opening 231 in a step ofpressing the protrusion 9 onto a portion of the bent region 232.

In the embodiment shown in FIG. 27 , the bent region 232 includes aportion arranged perpendicular to the insertion axis 235. This portion,in particular in combination with a protrusion that deforms when pressedagainst the portion, can direct the protrusion 9 towards the distalopening 231 in the step of pressing the protrusion 9 onto the portion ofthe bent region 232.

For example, the protrusion can include a deformation cavity 93 orregions of limited mechanical stability that favor a deformation of theprotrusion 9 in a predefined direction.

Alternatively or in addition, the protrusion 9 can include a deformationsurface 94 that is designed in a manner that a contact surface betweenthe protrusion 9 and the portion of the bent region 232 is establishedthat favors the deformation of the protrusion 9 in a predefineddirection.

FIG. 27 d shows an exemplary embodiment of such a protrusion 9. However,there is no need that the protrusion 9 includes a portion that is benttowards the distal opening 231 and/or a deformation cavity as long asthe portion of the bent region 232 against which the protrusion ispressed has a mechanical stability such that it is able to absorb themechanical load applied during the method.

For example, the protrusion 9 can straight or tapered and/orrotationally symmetric with respect to the protrusion axis 92.

One can envisage that the portion of the bent region 235 that directsthe protrusion 9 towards the opening 231 is not perpendicular (i.e. at90 degrees) to the insertion axis 235, but at an angle smaller than 90degrees, for example between 30 and 80 degrees or between 50 and 80degrees.

A deformation of the protrusion 9 towards the distal opening 231 caninclude a softening or partial softening of the protrusion 9.

In a variant of the embodiments shown in FIGS. 26 and 27 , the thirdobject 30 provided does not include the through bore 230 and the bentregion 232 if present. Rather, the through bore 230 and the bent region232, if present, are produced in a further step of the method. Thisfurther step is performed after the step of bringing the distal surface32 of the third object 30 in contact with the proximal surface 4 of thesecond object 2, in particular.

FIG. 28 shows an exemplary embodiment of a first object 1 including aplurality of protrusions 9, wherein the summarized volume of allprotrusions 9 fulfills a condition for the volume.

In many embodiments including a plurality of protrusions 9, theprotrusions are arranged in a subarea of the area formed by the distalsurface 14 of the second object. The subarea defines a base 211 of theprotrusion region 90. In FIG. 28 , the base 211 is the area within thedashed line that on the distal surface 14.

The total volume of the protrusion region 90 can be calculated from thebase 211 and a value or function corresponding to or approximating theextension 25 of the protrusions 9 in distal direction.

In many embodiments (but not all, FIGS. 15, 16, 21-23 for example), theprotrusions 9 have an equal extension 25 in distal direction. In otherwords: they have an equal length. In this case, the value correspondingto the extension 25 of the protrusions 9 is their length.

The protrusions 9 within the protrusion region 90 are separated by gaps27, this means void space. This space fills the volume of the protrusionregion 90 not covered by the protrusions 9.

The volume condition fulfilled by the exemplary embodiment shown in FIG.28 , but also by many other embodiments of the first object 1, is thefollowing: The volume of the protrusions 9 is half of the volume of thevoid space or less. In other words: The volume of the protrusions 9corresponds to ⅓ or less of the total volume of the protrusion region90, for example ¼, ⅕ or less than ⅕, such as 1/10.

FIG. 29 shows an embodiment of the method in which the (or a) region 23of high density forms the proximal region of the second object 2 and theregion 22 of low density is arranged distally of the region 23 of highdensity.

Further, the optional feature of a support 63 that can be present duringbonding the first object 1 to the second object 2 only, or an item towhich the second object 2 is or will be attached, or an integral part ofthe second object 2.

FIG. 29 a shows the situation before bonding the first object 1 to thesecond object 2. FIG. 29 b shows the situation after bonding the firstobject 1 to the second object 2.

FIGS. 29 a and 29 b depict an embodiment of the second object 2 in whichthe region 23 of high density is compressible, too. This is indicated bythe doubled headed arrow that visualized the local compression of theregion 23 of high density caused by the impact of the first object 1that has been pushed through the region 23 of high density and that hasbeen anchored in the region 22 of low density.

The region 23 of high density is such that it is deformable, inparticular compressible. This allows for pushing in the first object 1in a manner that it does not protrude from the proximal surface 4 of thesecond object after bonding. Further, it results in a compression of theregion 22 of low density that is in addition to the compression effectedby the protrusion 9 penetrating the region 22 of low density. Again, itis this compressed region 201 that leads to an efficient liquefaction ofthe thermoplastic material 3.

In the embodiment shown, there is no need that the protrusion 9 gets incontact with the support 63 thanks to the compression of the region 22of low density.

In the embodiment of FIG. 29 , the body 7 of the first object 1 isreduced to a head.

FIG. 30 shows a sectional view of a first object 1 bonded to yet anothertype of the second object 2. According to this embodiment, the secondobject 2 provided is characterized by a proximal top layer 200 arrangedon a region 22 of low density, wherein the region 22 of low density isarranged on a region 23 of high density that is capable to givemechanical stability to the second object 2.

Such configurations including a proximal top layer arranged on a region22 of low density arranged on a region 23 of high density can be foundin items that must be rigid and comfortable to touch. Sometimes, suchitems are also called “softtouch” or items having a “softtouch surface”.

In embodiments, the proximal top layer is leather, artificial leather ora foil, and the region 22 of low density includes or consists of foam oranother porous and resiliently deformable material. The region 23 ofhigh density can then be any kind of a support.

An example of a “softtouch item” having the structure described is adashboard, for example a car dashboard.

As an example, FIG. 30 shows a first object 1 being a display elementthat is bonded to a second object 2 being a dashboard having thestructure described previously.

FIG. 30 a shows the second object 2 (the dashboard) as provided, thismeans including the proximal top layer 200 and the region 22 of lowdensity which is arranged on the region 23 of high density. The secondobject 2 provided includes further a feedthrough 207 designed toaccommodate the first object 1 (the display element) and wires 209 thatmay be present.

FIG. 30 b shows the situation after insertion of the first object (thedisplay element) into the second object 2 (the dashboard). The bondingmethod and the mechanism including a compressed region 201, a protrudingportion 91 and liquefied thermoplastic material 3 that has penetratedinto structures 10 of the region 22 of low density (e.g., the foam) isthe same as described previously.

Instead of mounting the first object 1 (the display element, forexample) as a whole, one can also envisage to bond a connector 16 to thesecond object 2 first and the actual element to be attached to thesecond object 2 in a subsequent step. This embodiment is indicated inFIG. 30 b by dashed lines.

In this embodiment and using the example of the display element to bemounted to the dashboard again, the first object 1 is the connector 16and the display element is a third object 30 to be mounted to secondobject 2, this means to the dashboard, by the use of the first object 1.

For example, the connector 16 includes an element 15 for attaching thedisplay element (the third object 30) to the connector 16, for exampleby a clamping mechanism.

The protrusions 9 can be designed to penetrate the proximal top layer200 without need for a preceding perforation of the proximal top layer200. In particular, the protrusions 9 can be designed to penetrate theproximal top layer 200 without becoming flowable.

It goes without saying that the first object 1 attached to the secondobject 2 characterized by the proximal top layer 200 arranged on theregion 22 of low density can be any embodiment of the first object 1disclosed, for example a connector. In this case, the second object 2does not include any features that are specific for mounting the displayelement. For example, it does not include the feedthrough 207.

FIG. 31 shows a sectional view of a third object 30 being attached tothe second object 2 including a region 22 of low density by a firstobject 1, wherein the first object 1 includes a head 212 and aprotrusion 9 that is arranged distally of the head 212.

The third object 30 can include a pre-drilled opening or the thirdobject 30 and the protrusion 9 can be designed such that the protrusioncan penetrated the third object 30 in a step of pressing the firstobject 1 towards the third object 30.

The head 212 is designed in a manner that a portion of the third object30 is clamped between the head 212 and the second object, in particularthe proximal surface 4 of the second object 2.

Again, bonding of the first object 1 to the second object 2 isestablished by the generation of a compressed region 201 during the stepof pushing the protrusion 9 into the second object 2.

FIGS. 32 a and 32 b shows an embodiment of the method including thefurther step of providing an adhesive 240 prior to the step of pushingthe protrusion(s) 9 into the second object 2.

FIG. 32 a shows the situation after providing the adhesive 240 on theproximal surface 4 of the second object 2.

In this embodiment, the first object 1 can include, as an optionalfeature, a retention protrusion 213 arranged in the region of thelateral end of the body 7. The retention protrusion 213 protrudes fromthe distal surface 28 of the body 7 into the distal direction.

The retention protrusion 213 is designed to prevent the adhesive 240 tobe pressed laterally beyond the lateral extension of the first object 1,in particular the first object body 7. In other words: the retentionprotrusion 213 is designed to prevent a reduction of the amount ofadhesive contributing to the bonding of the first object 1 to the secondobject 2 during the bonding process.

In particular, the retention protrusion 213 prevents a contaminationwith adhesive 240 of areas of the proximal surface 4 of the secondobject 2 that are external areas after the bonding process.

The retention protrusion 213 as well as the protrusions 9 can defineretention openings 214 in which adhesive can accumulate.

FIG. 32 b shows the situation after bonding the first object 1 to thesecond object 2 by the method including the further step of providing anadhesive 240.

The adhesive 240 is pressed into the second object 2 during the step ofpressing the first object 1 into the second object 2. Hence, a zone 241penetrated by adhesive 240 is generated around the protrusions 9, atleast. In this zone 241, the material forming the region of low density22 is augmented by the adhesive. For example, the region of low density22 includes fibers that are stuck together due to the presence of theadhesive.

Hence, the further step of providing the adhesive 240 is a furtherapproach to improve the quality, in particular the mechanical stabilityand reliability, of the first object 1 being bonded to the second object2 by the method.

FIGS. 33 a and 33 b show another exemplary embodiment of a first object1 being a connector 16.

The connector 16 shown includes the protrusion region 90 with aplurality of protrusions 9 and a connecting structure defining aconnecting location defined with respect to all dimensions (x, y, z).The connecting structure in the depicted embodiment is constituted by aconnector peg 250 that is one-piece with the protrusions 9 and the body7.

The connecting structure—the connector peg 250 in the shownembodiment—is especially such that it is arranged laterally. This meansthat the arrangement of the connecting structure 250 is not symmetricalwith respect to the insertion axis 235 but is off-center with respect tothe axis 235. The insertion axis 235 is the axis along which generallythe pressing force is applied during insertion and along which themovement during insertion will take place at least predominantly. Theinsertion axis 235 is generally a characteristic axis of the firstobject, such as a rotation axis, a central axis and/or it coincides withthe protrusion axis. The latter can be the case when the first object 1includes a single protrusion 9 or a central protrusion 9. Thus, the axisis especially defined by the protrusion and/or the overall shape of thefirst object 1.

Thereby, the position of the connecting location depends on the angle ofrotation around the axis 235. Hence, when the connector is positionedrelative to the second object 2 and anchored therein, not only theposition but also its orientation may have to be defined.

An example of an according connecting structure may, for example, be astructure (like the peg) that protrudes away from the protrusion(s) intoa defined direction, such as a pivot of a hinge or similar, a structurefor clipping another item onto, an anchor for a thread connection, etc.

The connector 16 of FIGS. 33 a and 33 b includes a plate-like body 7defining the distally facing stopping surface 12. From the body 7towards proximally, the connector includes a base wall 253 from whichthe connector peg 250 protrudes laterally. The base wall is arrangedoff-center with respect to the axis 235. Further, the connector includesa plurality of reinforcing walls 254 extending perpendicularly to thebase wall 253 and enhancing the mechanical stability with respect toforces acting on the connector peg.

The distally facing stopping surface defines the z position of theconnecting structure after the process in that the pressing force isapplied until the stopping surface 12 abuts against the proximal surface4 of the second object 2.

The connector 16 in the embodiment of FIGS. 33 a and 33 b may, forexample, be a mount of a rear parcel shelf of an automobile.

The sonotrode 20 used for anchoring the connector may be shaped to beadapted to the shape of the connector. Especially, as shown in FIG. 33 a, the connector may be shaped to impinge, from proximally, on the body 7by engaging between the reinforcing walls 254 and the base wall 253. Inaddition or as an alternative, it would also be possible to provide aprotruding collar 255 of the connector 16, as shown in dotted lines inFIG. 33 a . The arrangement with the sonotrode engaging between thewalls directly on the body 7, with the sonotrode having indentations forreinforcing wall(s) if necessary, though, features the advantage thatthe pressing force and vibration (more generally the mechanicalexcitation) are coupled straight into the protrusions.

In embodiments that include a connecting location the position and/ororientation of which depends on the orientation of the connector aroundits axis 235, it may be necessary to guide the orientation of theconnector during the anchoring process, because due to the vibrationinput (more generally the mechanical excitation) the connector may besubject to some uncontrolled twisting movements during insertion. In theembodiment of FIGS. 33 a and 33 b , the base wall 253 and/or thereinforcing walls 254 may be used for this, together with acorresponding shape of the sonotrode, whereby the orientation of thesonotrode defines the orientation of the connector.

The exemplary embodiment of FIGS. 33 a and 33 b includes further theoptional feature of a cutting structure 252 that is designed topenetrate a proximal top layer, for example.

The embodiment of FIG. 33 , but also of FIG. 7 , for example, includesusing a sonotrode adapted to the geometry of the first object 1 being athe connector. This is not always necessary. One can envisageembodiments of a first object 1 being a connector in which the body 7forms a generally flat coupling surface for a generic sonotrode.

The connector can include at least one process controlling abutmentprotrusion if the number and/or arrangement and/or dimensions of theprotrusions 9 are such that the connector cannot be held in a desiredposition relative to the second object at the beginning of applying amechanical pressing force and—as the case may be—the mechanicalexcitation. This abutment protrusion(s) together with the protrusionscan give a stable standing to the connector when the connector isbrought into contact with the proximal surface of the second object. Inother words: the connector position is well-defined and stable.

An abutment protrusion of this kind may, during the subsequent process,collapse or melt away. It does not necessarily have to penetrate intothe volume of the second object.

In addition to stabilizing the connector during an initial stage of theprocess, it can also dampens undesired bending vibrations when the body7 has a substantial lateral extension.

FIGS. 34-39 show various exemplary embodiments of the protrusion region90 of the first object 1 and the device, respectively.

In the exemplary embodiment shown in FIG. 34 , the protrusions 9 includea protrusion axis 92 that does not run parallel to the normal of thedistal surface 28 of the body 7 of the first object 1.

The protrusion axis 92 running not parallel to the normal defines adirection into which the protrusion 9 deforms during the method in anyone of the embodiments disclosed.

A further consequence of the protrusion axis 92 that does not runparallel to the normal of the distal surface 28 of the body 7 of thefirst object 1 is that the length of the protrusion is larger than theextension 25 of the protrusion in distal direction.

At least the following features are shown in the exemplary embodimentsof the first object 1 depicted in FIGS. 34-39 :

-   -   The functional region 50. In the embodiments of FIGS. 38 and 39        , the functional region is given by the distal mouth of a        through bore that extends from the proximal surface 29 to the        distal surface 28 of the body 7 of the first object 1.        -   A first object 1 including a through bore can be applied for            stabilising or fixing the edge of the feedthrough            established, e.g., punched into the second object 2.    -   The gaps 27 between the protrusions 9, wherein the volume of the        gaps and the volume of the protrusions have the ratio described        above.    -   An extension 25 of the protrusion 9 in distal direction and a        thickness 26 of the protrusion 9 that are such that the ratio        between the extension 25 and the thickness 26 is as described        above, this means at least 1, in particular between 1 and 5, for        example between 1.5 and 4 or between 2 and 3.

FIGS. 40-43 show perspective views of various exemplary embodiments ofthe first object 1 and the device, respectively.

Various connection elements 15 of a connecting device are shown inaddition to the features related to the protrusion region 90. Theelements are arranged on the proximal surface 29 of the body 7 of thefirst object 1.

The embodiments shown include a connection location 51 at which theelements 15 of the connecting device are connected to the first object1. In the embodiments shown, the connection location 51 includes and isrestricted to a portion of the proximal surface 29 of the body 7 of thefirst object 1 that is opposite to the functional region 50 arranged onthe distal surface 28 of the body 7 of the first object 1.

The connection element 15 of the first object 1 shown in FIG. 40 issuited for attaching cables and/or wires to the first, and hence to thesecond, object.

The connection element 15 of the first object 1 shown in FIG. 42 is anexample of a connection element suited for screwing an item to thefirst, and hence to the second, object. The connection element shown caninclude a longitudinal opening that goes through to the distal surface28 of the body 7 the first object 1.

The connection element 15 of the first object 1 shown in FIG. 42 issuited for attaching plate- and/or sheet-like items to the first, andhence to the second, object.

The connection element 15 of the first object 1 shown in FIG. 43 is anexample of a connection element for clip solutions.

First objects 1 as shown in FIGS. 34-43 , for example, are bonded to thesecond object 2 by the use of a sonotrode 20 that is applied at theportion of the proximal surface 29 of the first object 1 not covered bythe connection element 15 or any element of a connecting device,usually. Further, the mechanical excitation, this means the mechanicaloscillations, are preferably applied along the axis 8 that runs at anangle, in particular normal, to the proximal surface 29.

In this case, the coupling-out face 21 of the sonotrode 20 extendspreferably over an area of the proximal surface 29 of the first object 1during the step of applying the mechanical pressing force and themechanical excitation that is comparable with the opposite area coveredby protrusions 9 on the distal surface 28 of the first object 1. Forexample, the area in contact with the coupling-out face 21 covers atleast 80% of the area covered by protrusions on the distal surface 28 ofthe first object 1. For example, it extends over an area that is 0.8 to2 times the area covered by protrusions 9, in particular 0.8 to 1.5, 0.8to 1.2 or 0.8 to 1 times. In other words: the radial extension of thearea of the proximal surface 29 is at least 80% of, in particular largerthan, the radial extension of the area covered by protrusions on thedistal surface 28 in any radial direction.

The coupling-out face 21 can protrude over the body 7 of the firstobject 1.

FIGS. 44-49 show exemplary embodiments of first objects 1 that includefeatures capable to prevent the generation of natural oscillation in thefirst object body 7 of a strength that can be destructive for the firstobject body 7.

The embodiment according to FIG. 44 includes a damping element 52arranged at the distal surface of the first object body.

The damping element 52 gets in contact with the proximal surface 4 ofthe second object 2 or—as the case may be—with the proximal surface 31of the third object 3 during the method of bonding the first object 1 tothe second object 2. Thereby, natural oscillation generated in the firstobject body 7 during the step of applying the mechanical excitation toliquefy the thermoplastic material 3 can be damped due to the physicalcontact generated between the damping element 52 and the second 2 or—asthe case may be—the third object 3.

In the embodiment shown, the damping element 52 includes thermoplasticmaterial, too. In other words, the damping element 52 is not onlycapable to damp the natural oscillation but also to enhance the bondingbetween the first and second (or third) object.

The embodiments according to FIGS. 45 and 46 include a plurality ofdistinct protrusion regions 90 that are designed to minimize the energyof the mechanical excitation needed to liquefy the thermoplasticmaterial.

Further, FIGS. 45 and 46 each show a set of protrusion regions capableto tune away the frequency of the natural oscillations of the firstobject body 7 from the frequency applied to cause liquefaction of thethermoplastic material.

At least one of the protrusion regions 90 can be arranged to act as adamping element 52 too, as shown in FIGS. 45 and 46 . However, it is notmandatory that one protrusion region of the plurality of protrusionregions is designed and arranged as a damping element 52.

FIGS. 47 and 48 show a first object 1 including a fixation element 1.1designed to be bonded to the second object 2 by a method according tothe invention and a connecting element 1.2 designed to be bonded to thefixation element 1.1.

The fixation element 1.1 includes a fixation element connection means110 and the connecting element 1.2 includes a connecting elementconnection means 120 that are adapted to one another in a manner thatthe bond between the fixation element 1.1 and the connecting element 1.2can be established.

In the embodiment shown, the fixation element connection means 110 is athrough hole in the body 7.1 of the fixation element 1.1 and theconnecting element connection means 120 is a protrusion with a diameteradapted to a diameter of the through hole.

The protrusion 120 includes thermoplastic material and is designed in amanner that it can be bonded to the second object 2 after being pushedthrough the through hole 110 in the body 7.1 of the fixation element1.1.

In addition or alternatively, the protrusion 120 includes thermoplasticmaterial and is designed in a manner that it can weld to thermoplasticmaterial of the fixation element 1.1, in particular of thermoplasticmaterial 3 of the protrusions 9 designed to bond the fixation element1.1 to the second object 2 by the method.

One can also envisage other means for bonding the connecting element 1.2to the fixation element 1.1, for example clamping means, clipping meansand/or the elements of a bayonet lock.

FIG. 49 shows the fixation element 1.1 of a first object 1 including afixation element 1.1 and a connecting element 1.2 in detail.

The body 7.1 of the fixation element 1.1 and of the correspondingconnecting element 1.2 includes thermoplastic material. The fixationelement 1.1 includes a fixation element energy director 111 and theconnecting element 1.2 includes possibly a connecting element energydirector 120. Such energy director (111 and 120) define a region wherethermoplastic material of the fixation element 1.1 and of the connectingelement 1.2 liquefies in a further step of applying a mechanicalpressing force and mechanical excitation.

The further step causes a connection (in particular, a weld) between thefixation element 1.1 and the connecting element.

In particular, the further step is applied after the step of applyingthe mechanical pressing force and the mechanical excitation causingliquefaction of thermoplastic material of the protrusion(s). This means,the further step is applied after bonding the fixation element 1.1 tothe second object 2.

An advantage of a method including two steps of applying mechanicalpressing force and mechanical excitation, a first one for bonding thefixation element 1.1 to the second object 2 and a second one for bondingthe connection element 1.2 to the fixation element 1.1, is at least oneof the following:

-   -   The energy acting on portions of the first object 1 that bear        the element of a connecting device 15 can be reduced;    -   The coupling-out face 21 of the sonotrode 20 can be adapted to        the shape of the fixation element 1.1 and/or the shape of the        connection element 1.2;    -   Any issue based on a frequency of a natural oscillation of the        first object body 7 close to the frequency of the mechanical        excitation needed during bonding the first object 1 (this means        the fixation element 1.1) to the second object 2 can be avoided.

FIGS. 50 and 51 show a further method for fixing a third object 30 tothe second object 2 by the first object 1.

According to this method (FIG. 50 ) the third object 30 is glued on theproximal surface 29 of the first object body 7.

A first object 1 designed for use in the method according to FIGS. 50and 51 includes a proximal surface 29 that extends over a wide area.FIG. 51 shows such a first object 1. In particular, the first objectbody 7 forms an area on which the third object 30 can be fixed.

In addition, the first object 1 designed for use in the method accordingto FIGS. 50 and 51 can include any one of the features for preventingdestructive natural oscillations presented with respect to FIGS. 44-48 .

First objects 1 in any of the embodiments discussed above, for exampleas shown in FIGS. 1-5, 14, 16, 17, 20, 26 a, 28, 29 a, 31 and 34-43, canbe used to attach a third object 30 to the second object 2.

In particular, the third object 30 can be a sheet material, for examplea metal sheet.

The attachment of the third object 30 can include the at least localcompression of the second object 2, wherein the compression is in amanner that the critical density and/or the critical compressivestrength is generated.

FIG. 52 shows a sectional view of the arrangement and design of a firstobject 1, a second object 2 and a sheet material 30, wherein the sheetmaterial 30 is to be fixed to the second object 2 by the first object 1.

The sheet material 30 shown includes through bores 230 that are adaptedin shape and number to the protrusion(s) 9 of the first object 1.

For example, the protrusions 9 can be ridges as shown in FIGS. 1 and 5 ,for example. In this case, the sheet material 30 can include throughbores 230 in the shape of longitudinal slits.

For example, the first object 1 can include a protrusion region 90 asshown in FIGS. 5, 28, 34, 36 and 37 for example. In this case, the sheetmaterial 30 can include through bores 230 with a round or rectangularfootprint.

For example, the first object 1 can include a protrusion region 90 asshown in FIG. 35 , for example. In this case, the sheet material 30 caninclude through bores 230 in the shape of circular slits.

The through bores 230 can be such that a position of the sheet material30 relative to the first object 1 can be adjusted. In the case of afirst object 1 including a protrusion region 90 with a plurality ofprotrusions 9 that are arranged along a line, the sheet material 30 caninclude per line of protrusions 9 a through bore 230 in the shape of alongitudinal slit.

FIG. 53 shows a sectional view of a further arrangement and design of afirst object 1, a second object 2 and a sheet material 30, wherein thesheet material 30 is to be fixed to the second object 2 by the firstobject 1.

According to this exemplary arrangement, the first object 1 can includeat least two protrusions 9 and the corresponding method includes thestep of arranging the first object 1, the second object 2 and the thirdobject 30 such that at least one protrusion 9 is arranged beyond aradial end of the material sheet and at least one protrusion 9 is incontact with the proximal end of the third object 30.

Third object 30 can include a through bore 230 of the kind describedwith respect to FIG. 52 and the first object 1 can be arranged relativeto the second object such that at least one protrusion engages with thethrough bore 230.

In the embodiment shown, the third object 30 includes a flange 237designed for being positioned on the second object and for beingattached to the second object by the first object. The flange 237includes the through bore 230.

In particular, the first object 1 can be as shown in FIGS. 1-5, 20, 28and 34-43 , for example.

In the embodiment of FIG. 53 , the third object is a metal sheet. If thethird object 30 is a metal sheet, the metal sheet 30 is or can be heatedduring the method. This can cause local melting of the second object 2,which leads to a further increase in density of the region of lowdensity 22 and a further reinforcement thereof. In other words, thesecond object 2 can be transformed locally to a coherent material.

FIGS. 54 a and 54 b visualize a method for fixing a third object 30 thatis a metal sheet to the second object 2, wherein the metal sheet 30 hasno through bores 230 for the protrusion(s) 9.

The method includes the further steps of:

-   -   Arranging the first object 1, the second object 2 and the metal        sheet 30 relative to each other such that the proximal surface        31 of the metal sheet 30 is in contact with the protrusions 9        and such that the distal surface 32 of the metal sheet 30 is in        contact with the second object 2.    -   Pressing the first object 1 to the metal sheet 30 such that the        first object 1 and the metal sheet 30 are vibrationally coupled        to each other.    -   Applying the mechanical vibrations to the first object 1 and        increasing the pressing force such that the metal sheet 30        deforms into the second object 2.    -   Increasing the pressing force further until the protrusion(s) 9        penetrate the metal sheet 30. In other words, a penetration        region 260 is generated in the metal sheet 30.    -   Liquefaction of the thermoplastic material that has penetrated        the metal sheet in the compressed region 201 of the second        object and/or pressing the liquefied thermoplastic material in        the compressed region 201.

This embodiment of the method is appropriate for material sheets ingeneral. However, application of this method to metal sheets 30 has theadvantage that the metal sheet heats the second object 2 during themethod. This can cause local melting (melting zone 261) of the secondobject 2, which leads to a further increase in density of the compressedregion 201 and to further reinforcement of the region of low density 22.In other words, the second object 2 can be transformed locally to acoherent material.

FIG. 55 shows an exemplary embodiment of a first object that can be usedin the method according to FIGS. 54 a and 54 b . The embodiment shownincludes:

-   -   A first row of protrusions and a second row of protrusions. In        the embodiment shown, the protrusions of the first row have the        same length than the protrusions of the second row. Further the        protrusions are tapered.    -   A first region 263 on the distal surface of the first object 1        that is offset in distal direction from a second region 264 on        the distal surface. In the embodiment shown, the second region        264 (central region) is more distal than the first region 263        (region between the two rows of protrusions).        -   In particular, the more distal region is arranged to damp            natural oscillations during the method, in particular during            a final phase of the method when the energy coupled into the            objects is highest.    -   A channel 262 for material flow.

A first object as shown in FIG. 55 can help to avoid destructive naturaloscillations and destructive deformations of the third object 30, inparticular if the third object is a metal sheet 30.

FIG. 56 shows a sectional view of a basic arrangement of the first andsecond object for an embodiment of the method in which the sonotrode 20is applied to the second object 2.

In the exemplary arrangement shown, the first object 1 is an item towhich the protrusions 9 are connected. One can envisage configurationsin which the proximal surface 29 of the first object 1 is not or noteasily accessible. For example, the item can be a part of a car body.

In particular in such configurations, the second object 2 can be placedrelative to the protrusions 9 such that the protrusions 9 are in contactto the portions of the second object 2 that should be penetrated by theprotrusions 9 at least partly during the method.

In the embodiment shown in FIG. 56 , the second object 2 is a coverincluding a first region 204 of low density that forms an open layingsurface and a second region 205 of low density in which the positive-fitconnection between the first and the second object is to be formed.However, this structure is not mandatory for the method/applicationshown in FIG. 56 (and FIGS. 57 a and 57 b ). The second object 2 canhave a more sophisticated structure or it can be homogeneous.

FIGS. 57 a and 57 b show an exemplary application of the embodiment ofthe method in which the sonotrode 20 is applied to the second object 2.

FIG. 57 a shows the arrangement of first object 1, second object 2 andsonotrode before the step of applying the mechanical pressing force andthe mechanical excitation capable to liquefy the thermoplastic material.

FIG. 57 b shows the situation after bonding the first object 1 to thesecond object 2.

FIGS. 57 a and 57 b show:

-   -   A second object 2 that is a cover for the first object 1, for        example a part of a car body, wherein the cover is adapted or        adaptable in shape to the first object 1.    -   A plurality of protrusions 9 that are arranged on the first        object 1 in a manner that the cover 2 can be reliably fixed to        the first object 1.    -   The item 2 that is arranged on the first object 1 such that        bonding locations on the proximal surface 4 of the item 2 are in        contact with the protrusions.    -   The sonotrode 20 that is applied locally and sequentially to        regions of the distal surface 14 of the item 2 that correspond        to positions of the protrusions 9.        -   The sonotrode is applied to the item 2 until the item has            reached a desired end position relative to the first object            1.

FIG. 58 shows a variation of the method in which the second object 2 isplaced between the first object 1 and the sonotrode 20.

According to this variation, any force for advancing the protrusion(s) 9into the second object 2 is applied to the first object 1 (indicated bythe arrow below the first object 1).

The sonotrode 20 is in contact to the distal surface 14 of the secondobject 2 and couples mechanical oscillations into second object 2.Further, it acts as a support for the second object 2, but it does notpush actively the second object 2 towards the first object 1.

This arrangement of applying the sonotrode to the second object 2 andany pushing force to the first object 1 has the effect that a compressedregion 201 is generated around the protrusion(s), wherein thecompression of the distal surface 14 of the second object 2 is keptminimal.

FIG. 59 shows two stress-strain-curves (A and B) that are representativefor the experimental results that led to the surprising finding thatvarious incoherent materials are suitable for use in bonding methodsrelying on the liquefaction of thermoplastic material by the use of amechanical pressing force and a mechanical excitation, in particularvibrations.

The relative behaviour of stress-stain curves A and B shows theinfluence of a changing surface via which load is applied to thematerial. The indenter of curve B has a larger surface area in contactwith the material that the indenter of curve A.

FIG. 59 shows the observed first region in which the stress dependsapproximately linear on strain, the observed transition region and theobserved second region in which the stress depends approximately linearon strain.

The straight lines that approximate the approximately linear dependencein the different regions of linear dependencies are represented asdashed lines.

The strain cc at which the slope of the first region of approximatelylinear dependency and the slope of the second region of approximatelylinear dependency cross is a characteristic value of the stress-strainbehaviour of the material. The characteristic value can be used todefine a minimal compression needed in embodiments of the method inwhich the positive-fit connection is to be established in the region oflow density.

What is claimed is:
 1. A method of bonding a first object to a second object, the method comprising: providing the first object, wherein the first object extends between a proximal end and a distal end and comprises a first object body and at least one protrusion distally of the first object body, wherein the protrusion forms the distal end and comprises thermoplastic material in a solid state, providing the second object comprising a proximal surface, applying a mechanical pressing force and a mechanical excitation capable to liquefy the thermoplastic material to at least one of the first and second objects until a flow portion of the thermoplastic material is flowable, stopping the mechanical excitation and letting the thermoplastic material resolidify to yield a connection between the first and the second object, wherein the second object provided comprises a region of low density, wherein the protrusion penetrates the region of low density at least partly before the thermoplastic material is made flowable, wherein the first object comprises a protruding portion after the step of letting the thermoplastic material resolidify, wherein the protruding portion penetrates the region of low density at least partly, wherein the method comprises a step of changing a compressive strength of the region of low density at least locally such that a critical compressive strength needed for the liquefaction of the thermoplastic material is generated, wherein changing in the compressive strength is increasing the compressive strength from a compressive strength that is below a critical compressive strength needed for liquefaction of the thermoplastic material to a compressive strength that is above the critical compressive strength needed for liquefaction of the thermoplastic material, and wherein the second object comprises synthetic fibers or a thermosetting polymer.
 2. The method according to claim 1, wherein the method comprises a step of compressing the region of low density at least locally such that a critical density needed for the liquefaction of the thermoplastic material is generated.
 3. The method according to claim 1, wherein the second object provided comprises a density profile that increases as a function of the distance from the proximal surface, and in that the distal end penetrates the region of low density before the thermoplastic material is made flowable.
 4. The method according to claim 1, wherein the step of providing the first object comprises providing a first object comprising a protrusion region distally of the first object body, wherein the first object body comprises a distal surface and wherein the protrusion region comprises a plurality of protrusions that comprises the thermoplastic material.
 5. The method according to claim 4, wherein the first object comprises at least one protrusion of a first kind comprising the thermoplastic material and at least one protrusion of a second kind comprising the thermoplastic material, wherein an extension in distal direction of the protrusion of the first kind is larger than a corresponding extension in distal direction of the protrusion of the second kind such that the connection established by the protrusion of the first kind is at a different distal position than the connection established by the protrusion of the second kind.
 6. The method according to claim 4, wherein the protrusion region further comprises gaps between the protrusions, wherein the distal surface of the first object body forms a base of the protrusion region, wherein the protrusion region has a total volume given by the surface area of said base and by an extension of the protrusion region in distal direction, wherein the total volume consists of the volume of the plurality of protrusions and of the volume of the gaps, wherein the volume of the gaps is larger than the volume of the protrusions.
 7. The method according to claim 4, wherein at least one protrusion is at least one of equipped for deforming in a deformation direction during the step of applying the mechanical pressing force and the mechanical excitation, equipped for defining a direction into which liquefied thermoplastic material flows during the step of applying the mechanical pressing force and the mechanical excitation, and comprising a protrusion axis that runs at an angle to the distal surface of the first object body, wherein said angle is not a right angle.
 8. The method according to claim 1, wherein the mechanical pressing force and the mechanical excitation are applied locally to at least one of the first and second object and wherein the step of applying the mechanical pressing force and the mechanical excitation and the step of stopping the mechanical excitation and letting the thermoplastic material resolidify is repeated several times at different positions on at least one of the first and second object.
 9. The method according to claim 1, further comprising the step of providing a third object comprising a third object proximal surface and a third object distal surface and the steps of: arranging the third object relative to the second object such that the third object distal surface is in physical contact with the proximal surface of the second object; forcing at least a portion of the first object through the third object from its proximal face to its distal face prior to the step of applying the mechanical excitation capable to liquefy the thermoplastic material and to cause the flowable portion of the thermoplastic material to penetrate into structures of the second object.
 10. The method according to claim 9, wherein the first object comprises at least one protrusion of a first kind comprising the thermoplastic material and at least one protrusion of a second kind comprising the thermoplastic material, wherein the shape of the protrusion of the first kind is such that the flowable portion of the thermoplastic material penetrates into the structures of the second object, and wherein the shape of the protrusion of the second kind is such that a flowable portion of the thermoplastic material penetrates into structures of the third object during the step of applying the mechanical pressing force and the mechanical excitation capable to liquefy the thermoplastic material.
 11. The method according to claim 1, further comprising the step of providing a third object comprising a third object proximal surface and a third object distal surface and the steps of: arranging the third object relative to the second object such that at least a portion of the third object distal surface is in physical contact with the proximal surface of the second object; forcing at least a portion of the protrusion through the third object from its proximal face to its distal face; wherein at least one of the following conditions applies: the third object is a metal sheet comprising a through bore; the third object is a foil, wherein the foil is designed to be penetrable by the protrusion; the third object comprises a thickness and a density profile such that the protrusion can penetrate the third object during the step of applying the mechanical pressing force and the mechanical excitation but without causing the thermoplastic material to liquefy within or at a surface of the third object.
 12. The method according to claim 1, wherein the first object body comprises a proximal surface of the first object body, the method comprising further the step of providing a third object comprising a third object proximal surface and a third object distal surface and the step of arranging the third object relative to the first object such that the third object distal surface is in physical contact with the proximal surface of the first object body.
 13. The method according to claim 12, comprising the further step of gluing the third object distal surface to the proximal surface of the first object body.
 14. The method according to claim 1, wherein the method comprises the steps of providing a sonotrode and of arranging the first object, the second object and the sonotrode relative to each other in a manner that the second object is between the first object and the sonotrode and such that the proximal surface of the second object is in contact with the at least one protrusion or gets in contact with the at least one protrusion during the method.
 15. The method according to claim 1, wherein the second object comprises a distal surface and wherein the first object provided as well as the step of applying the mechanical pressing force and the mechanical excitation are such that the distal surface of the second object is unaffected by the method.
 16. The method according to claim 15, wherein the mechanical excitation is applied to the distal surface of the second object and a force for advancing the at least one protrusion into the region of low density is applied to the first object.
 17. The method according to claim 1, wherein the step of providing the second object comprises providing a second object comprising thermoplastic material and wherein said thermoplastic material liquefies at least partly during the step of applying the mechanical excitation such that a weld is formed by said liquefied thermoplastic material and liquefied thermoplastic material of the first object after resolidification of the thermoplastic materials.
 18. The method according to claim 1, wherein the second object is provided within a mold that is adapted to a desired shape of the second object and wherein the step of applying the mechanical pressing force and the mechanical excitation is carried out on the second object supported by the mold.
 19. The method according to claim 1, further comprising the step of providing a further object, wherein the first object body is designed to form a connection with a further object.
 20. The method according to claim 19, wherein the first object body comprises the proximal surface, the distal surface and a connection location, wherein the connection location comprises at least a portion of the proximal surface of the first object body, wherein the first object comprises the protrusion region arranged at the distal surface of the first object body and comprising the functional region that does not comprise any protrusions, and wherein the functional region is opposite of the proximal surface portion comprised by the connection location.
 21. The method according to claim 1, wherein the step of applying the mechanical pressing force comprises applying a first mechanical pressing force and a second mechanical pressing force, wherein the first mechanical pressing force is smaller than the second mechanical pressing force or equal to it.
 22. A device for being bonded to an item by a method according to claim 1, the device being the first object and the item being the second object, wherein the device extends between a proximal end and a distal end and comprises a device body and at least one protrusion distally of the device body, wherein the protrusion forms the distal end and comprises thermoplastic material in a solid state, wherein the device comprises a structure designed and arranged to promote a local compression of the item that is sufficient for liquefaction of the thermoplastic material when forced into said item.
 23. The device according to claim 22, wherein the device is a connector.
 24. The device according to claim 22, wherein the device comprises a protrusion of a first kind and a protrusion of a second kind, wherein the protrusion of the first kind is designed for being anchored in the item and the protrusion of the second kind is designed for being anchored in a third object different from the item.
 25. The device according to claim 22, wherein the device is a reinforcement element.
 26. The device according to claim 22, comprising at least one of the following features capable to avoid destructive natural oscillations: a damping element arranged at the distal surface of the device body; a fixation element comprising fixation element connection means and a connecting element comprising connection element connection means, wherein the fixation element connection means and the connection element connection means are adapted to each other in a manner that the connection element connection means can be rigidly connected to the fixation element connection means at least when the fixation element is fixed to the item; a plurality of protrusion regions that are separate from each other; a device body being non-homogenous in its physical properties.
 27. The method according to claim 1, wherein the flow portion of the thermoplastic material penetrates into structures of the second object when being flowable by applying the mechanical pressing force and the mechanical excitation, and a positive-fit connection between the first and the second object is yielded by stopping the mechanical excitation and letting the thermoplastic material resolidify. 